You know that saying "the left hand doesn't know what the right is doing"? For people with a strange disorder called alien hand syndrome, that's literally true -- the neuropsychiatric condition makes them feel as if one of their hands has taken on a mind of its own.

"An alien hand is an arm and hand that moves when the person to whom that arm belongs does not intend it to move," says Dr. Ken Heilman, a neurologist at the University of Florida College of Medicine in Gainesville, Fla. Heilman goes on to note that there are many neurological conditions that cause an arm to move unintentionally -- like seizures or tremors, and movement disorders such as chorea, dystonia and athetosis. Here's the difference: In each of those cases, if the arm moves, it's pretty much just flailing about purposelessly, "but with an alien hand, the movement appears to be purposeful." Creepy.

Heilman recalls one patient whose hands actually fought over fashion: Her right hand took a pair of red shoes out of the closet. Her left hand -- the "alien" hand -- pulled the red shoes out of her right hand, put them back and picked up a pair of blue shoes. When the right hand went again for the red shoes, the left hand slammed the closet door on the right hand.

A German neurologist and psychiatrist named Kurt Goldstein was the first to report a case of alien hand syndrome in 1908. His patient's left hand seemed to do whatever it pleased, including, at least once, an attempt to throttle its owner. It's most commonly the result of an injury to an area of the brain called the corpus callosum, which is, as Heilman describes it, "the major cable connecting the two hemispheres." (The injury often happens during surgery, such as an attempt to curb seizures, but it can also happen in stroke victims.) That injury prevents the two hemispheres from communicating, and because each side controls different behaviors and different hands, the confusion begins.

Usually, it's the left hand that is thought to be "alien," because that's the one controlled by the right hemisphere; the left hemisphere has no control over that hand, but it does control language, which gives the person the words to think, What is happening to my left hand?!

And it's always an alien hand, never an alien leg or foot. The brain has more bilateral control over the legs than it does the arms, Heilman explains. "The hand is this thing that does purposeful movement," he says. "We don't do a lot with our feet."

In one recorded case of alien hand syndrome, while a 67-year-old man slept, his hand did not; as a 1997 medical journal article reports, his hand "crept and crawled, especially at night, which caused him to awaken by grasping his collar." He solved his problem by wearing an oven mitt as he slept. But that guy had it easy. According to a 2000 journal article, a 73-year-old man's alien hand had a humiliating favorite hobby: masturbation.

Another more common (but less creepy) version of alien hand syndrome is an uncontrollable grasp reflex, which causes a patient to reach out and grab whatever is set in front of him, just like a baby would. (It's caused by an injury to the frontal lobe, which suppresses that grasping reflex as we mature.)

Alien hand syndrome is an extremely uncommon phenomenon -- most physicians have never even heard of it, says Heilman, who has only seen two patients exhibiting the more extreme kinds of symptoms. But it's popped up from time to time in pop culture.

The condition is sometimes known as "Dr. Strangelove syndrome," named for the titular character in Stanley Kubrick's famous 1964 film, in which Dr. Strangelove's right arm repeatedly tries to give a Nazi salute, and he must beat it down again and again with his left arm. More recently, "30 Rock's" live episode on Oct. 14 took on the spirit of the alien hand idea, featuring Jon Hamm in two fake, "Saturday Night Live"-style "commercials" for hand transplants gone totally wrong. (The late-1990s horror flick "Idle Hands" also nodded to the creepiness of the uncontrollable hand concept, but unless you, too, were a 14-year-old 8th grader in 1999 with a giant crush on Devon Sawa, you probably don't remember that one.)

In the real world, there isn't anything that can "cure" or even treat alien hand syndrome, Heilman says. Patients usually just come up with creative ways to keep their own appendages in check. "I had a patient who sat on his left hand," he says. "Many others treat their alien hand as if it were a disruptive child."

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You’ve seen them dance to Michael Jackson’s Thriller and read about their brain-eating adventures in the days of Jane Austen. There are zombie walks, zombie pub crawls and zombie flash mobs. Come Sunday, you’ll even be able to watch zombies in their own AMC TV series.

Yes, the walking dead are everywhere these days -- even in the mental disorders bible the DSM -- thanks to a rare neuropsychiatric disorder known as Cotard delusion, or walking corpse syndrome.

First described by French neurologist Jules Cotard in 1882, the delusion is linked to depression and brain injury in some cases, and thought to be neurologically related to Capgras delusion. In Capgras, a disconnect in the region of the brain that recognizes faces causes people to believe their loved ones are imposters. In Cotard’s, that disconnect results in them not recognizing their own face; as a result, they come to believe they’re dead.

But people with Cotard delusion don’t just think they’re dead. In advanced cases, they sometimes believe their flesh is beginning to rot or that some of their internal organs or their blood is missing.

Story: 'Walking Dead's' zombies are rising for TV dominance

In a case written about in the journal “Psychiatry” in 2008, a 53-year-old Filipino woman with Cotard delusion was admitted to a psychiatric unit after she told her family she was dead, smelled of rotting flesh and wanted to be taken to a morgue so she could be with other dead people.

Another case reported in 2008 involved a 28-year-old pregnant housewife from in Kashmir, India, who became increasingly depressed and eventually began telling people that her liver was “putrefying,” her stomach was missing and that her heart was “altogether absent.”

In another case from 2001, a 44-year-old man fell into a deep depression after he was unable to find work. Homeless, unemployed and unable to obtain psychiatric treatment, his symptoms worsened over a six-week period until he began to tell people that he had “melted away” and was “dead.” In the ensuing weeks, according to a letter in the journal Psychiatric Services, “his symptoms and daily functioning worsened. He continued to voice delusional beliefs, such as ‘my brain’s rotted away,’ ‘parts of my insides are gone’ and ‘I’m dead.’”

All three patients received treatment – and relief – through drugs and/or ECT (electroconvulsive therapy) and eventually came to realize they were not actually walking corpses.

But other individuals have not been as fortunate, particularly those who’ve fallen victim to a voodoo zombie curse. Practiced primarily in Haiti during the 18^th and 19^th centuries, the voodoo zombie ritual first involves slipping the potential victim a substance – usually a neurotoxin derived from the puffer fish -- in order to make it appear as if they’re dead. They’re then buried (sans embalming), and a day or two later, dug up and revived.

“But not to the point that they know who they are,” says Brad Steiger, author of “Real Zombies, the Living Dead and the Creatures of the Apocalypse.” “They’re in a perpetual trance, a twilight state. They’re brought back to serve as a slave for a voodoo priest or priestess.”

Steiger, who’s written about the paranormal for the last 50 years, says there have been many cases of "real-life zombies" over the years, many involving people who would spot a supposedly deceased relative working away in the sugar cane fields. He retells this spooky legend, which is included in his book: “There was a gentleman from Florida who went to Haiti and was dancing with a lovely young Haitian girl when he suddenly felt a prick on his arm,” he says. “He didn’t pay any attention to it, but the next thing he knew, he woke up with a hoe in his hand. He still had his suit and tie on but was working in the Haitian fields. Luckily, he was able to recover enough to eventually make it back to Florida.”

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Want to know what it’s like to be dead? Ask Julie Maeder, a 50-year-old certified image consultant from Troy, Mich.

"When I was 13 years old, I was in northern Michigan at my family’s cabin and came down with a 106 degree fever,” she says. “I remember trying to fall asleep and feeling too hot. And then I began to notice the room getting darker and the moonlight disappearing.”

After that, Maeder says, the really weird stuff began to happen. She started to float up towards the ceiling, even though her body was still lying on the bed. Her pain completely vanished and soon she was being pulled down a long, dark tunnel. At the end of the tunnel, there was a blinding white light and a sense of peace and calmness and utter joy.

“It was fantastic,” she says.

It’s also standard operating procedure for what Diane Corcoran calls a near-death experience, or NDE.

“There are about 15 characteristics that are universal in a near-death experience,” says Corcoran, president of the International Association for Near-Death Studies. “Some people will have one or two characteristics, some people have all 15.”

Corcoran says out-of-body experiences are just one hallmark of an NDE. Others include an immediate relief of pain, a feeling as if you’re traveling through a tunnel or to some other place, a feeling of being surrounded by bright light and an overwhelming sense of peacefulness. In addition, some people will see -- and even speak to -- departed relatives; others will see religious figures. Still more have talked about seeing flowers and hearing music -- and being filled with a tremendous sense of knowledge.

“Not everyone has all of them but we hear about these repeatedly,” she says. “There are also significant after-effects. People will come back with a whole different set of values; they’ll come back more affectionate and altruistic and less materialistic They’ll be more spiritual, although not necessarily more religious.”

The big question, of course, is whether the NDE is some kind of journey to the other side or whether it’s the body’s reaction to trauma. And there is evidence to support both theories.

Earlier this year, the medical journal Critical Care reported that Slovenian researchers had determined that people who reported near-death experiences had elevated levels of carbon dioxide in their blood and might be suffering from oxygen deprivation, the symptoms of which (particularly euphoria and the feeling of moving towards a light) can be similar to the symptoms of an NDE.

But Corcoran says studies attempting to debunk the millions and millions of NDEs that have been reported over the years are nothing new.

“People are always trying to find a reason to explain it away,” she says. “What usually happens is they can account for one or two of the characteristics, but they can’t account for all of the characteristics. How do you account for a 7-year-old who comes back knowing all about his dead grandfather from England who died in a fire, even though neither of his parents knew about it and the child has never left his own city block? Oxygen deprivation doesn’t account for those things.”

An international study launched in 2008 may provide more answers, though. Dubbed AWARE (short for Awareness During Resuscitation), the study will follow people who’ve gone into cardiac arrest in 25 hospitals in the U.S. and Europe. Researchers plan to monitor patients’ brain oxygen levels as well as test for out-of-body experiences, via a picture shelf installed high above the patients’ beds in cardiac ICUs (the patients will have to be “floating” outside of their body in order to see a photo on the shelf).

Unfortunately, results of the AWARE study won’t be released for at least two more years.

In the meantime, there’s always Clint Eastwood’s vision of the "Hereafter" to tide people over. Or experiences like that of Julie Maeder, who says that while her NDE happened nearly 40 years ago, it still resonates.

"When I told my parents about my experience after I woke back up in my bed the next morning, they said I must have been hallucinating because of the fever," says Maeder, whose fever broke at some point during the night when she saw the light. "But I still remember it. I’ll never forget it. And I can say that although I enjoy my life and don’t want to die any time soon, I’m not afraid of dying. I kind of think it’s going to be an unbelievable experience. I think we’re all going to a great place.”

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One January day in 2007, a terrifying idea seized a 45-year-old wife and mother in Omaha, Neb.: Her husband and teenage sons were not, in fact, her husband and teenage sons. Strangers who happened to be identical to her family members had taken over her home, and to fend them off, she armed herself with a fireplace poker, called her neighbors -- and 911.

It sounds like something out of the 1956 sci-fi film "Invasion of the Body Snatchers," but the Nebraska mom actually was suffering from something called Capgras delusion, a rare psychiatric disorder in which a patient believes her friends or family members are not who they say they are -- and that the real people have been replaced by identical-looking impostors.

Normally, we recognize faces thanks to a part of the brain called the fusiform gyrus, which is located in the temporal lobe. It processes the faces we see, and sends that information on to another part of the brain, the amygdala, which processes emotions. But in patients with Capgras, there's a disconnect between that visual center and the emotional center, explains Dr. Mariam Garuba, a New York psychiatrist who treated the Nebraska woman when she was admitted to an Omaha, Neb., emergency room three years ago. (Garuba wrote about the unusual case, referring to the patient only as "Ms. A," in a clinical psychiatry journal last year.)

In other words: Ms. A knew that these people standing in front of her looked, talked and acted like her husband and her children, but they didn't make her feel the way she usually did when she saw them.

It's worth noting that if Capgras patients talk to a loved one on the phone, they will recognize the voice. But if that loved one enters the room, the patient will accuse his friend or family member of being an impostor; that's because hearing and sight take different pathways to reach the brain's emotional center. (Extra credit: Watch neurologist V.S. Ramachandra deliver a fascinating speech on Capgras and other brain disorders at a 2007 conference.)

In some cases, that disconnect that is thought to cause Capgras is brought on by a head injury; in others, it's related to an existing psychiatric or neurological disorder. Ms. A falls in the latter group, as a longtime bipolar disorder patient who'd also been diagnosed with multiple sclerosis. Although she'd taken drugs to treat the bipolar disorder in the past, she was taking none in January 2007; she was also not taking any medication for her MS. Her physicians, including Garuba, believed the Capgras delusion occurred because of a relapse of Ms. A's MS. She was treated with antipsychotics, and after a few days, she gradually stopped believing that her doctors were trying to poison her; after nearly a month in the hospital, she stopped believing that her family members were impostors.

The rare disorder is named for Joseph Capgras, a French psychiatrist who was the first to write about the delusion in 1923, after treating a woman who became convinced that her husband and others she knew were actually body doubles. Similar cases to Ms. A's in recent years include a 24-year-old woman who, after some complications with pneumococcal pneumonia led to epileptic seizures, began to believe that some of the ICU physicians had been replaced by impostors. And in the UK, a 42-year-old woman claimed that while she was in the ICU for pneumonia in 1999, each of her family members except for her mother were replaced by aliens.

Of course, we don't know exactly how these patients voiced their suspicions, but it must have at least carried the spirit of this quote from the 1950s "Body Snatchers" trailer: "Listen to me! Please, listen! If you don't -- if you won't -- if you fail to understand -- then the same incredible terror that's menacing me will strike in you!"

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Beyond the traditional werewolf legends and the big, bad hotness of Jacob Black in the “Twilight” saga, is there any truth behind the notion of a man or woman actually transforming into an animal?

Yes and no, says Ben Radford, managing editor of the Skeptical Inquirer and author of “Scientific Paranormal Investigation: How to Solve Unexplained Mysteries.”

“There are conditions that are basically lycanthropic conditions,” says Radford, who has investigated ghosts, lake monsters, and mysteries like the chupacabra for a dozen years.

A likely physiological explanation for the werewolf legend is a genetic condition known as generalized hypertrichosis, which causes hair to grow excessively all over the body, including the hands and face, Radford suggests.

Although rare -- there have probably been only 50 described cases since the Middle Ages -- the condition has been well documented. In fact, lovelorn Mexican circus star Larry Ramos Gomez, better known as “Wolfboy,” is a Body Odd all- star for his efforts to develop a reality dating show (as of yet, the show hasn’t materialized).

In generalized hypertrichosis, all of the normally invisible hairs on the human body are replaced with thick coarse terminal hairs.

“There are apparently a very small number of people where virtually all the areas of the body that would have vellus hair seem to have terminal hair,” says Dr. Daniel Aires, director of the division of dermatology at the University of Kansas Hospital. “Those are the people who look like wolves.”

Other famous personages with generalized hypertrichosis include the so-called “Hairy Family of Burma,” Stephen Bibrowski, later known as "Lionel The Lion-faced Man," and Fedor Jeftichejev, more commonly known as Jo-Jo, the Dog-Faced Boy, a wildly popular Barnum & Bailey sideshow performer during the early 20^th century.

It can affect women, too. Julia Pastrana, the famous Bearded Lady of the mid 1800s, had a dual condition of generalized hypertrichosis with gingival hypertrophy, which caused excessive dark hairs all over her body as well as distorted facial features and enlarged gums.

Only last year, researchers discovered the genetic mutations responsible for the Bearded Lady’s rare condition.

Hypertrichosis isn’t the only possible basis for some of the werewolf myths. Cushing’s Syndrome, a hormonal disorder caused by high levels of cortisol in the blood, can cause symptoms of excessive hair growth, a fatty hump between the shoulders, pink or purple stretch marks on the skin and hyperhidrosis (excessive sweating). Then there’s porphyria, a blood disorder which makes people sensitive to light, may stain the teeth red and can lead to excessive hairiness.

“The combination of those things may have given rise to the Dracula or the Wolfman legends,” says Aires.

Psychological conditions may also be responsible for a little full moon hairy madness. “There are people living today who are absolutely convinced they’re werewolves,” says Radford.

The werewolf legend may make for spine-tingling fiction and smoking-hot movie characters, but, in the end, it traces back to a time when there were a whole lot of ‘monsters’ that wouldn’t be considered that way now.

“Basically, anything that made a person appear different would lead people to attribute that person to being a werewolf or a vampire. I’m well steeped in monster tradition but in terms of modern reports of werewolves, they’re not terribly common,” says Radford.

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Considering copying Lady Gaga's meat dress, which she wore to last month's MTV Video Music Awards, for your Halloween parties next week? A new video from the Newark, N.J.-based Star-Ledger explains why this is a terrible idea.

1. You will spread gross bacteria everywhere.

2. You will drip blood everywhere. As one New Jersey butcher told the reporter, "If it's fresh meat you're going to get blood, juice over everything you touch or sit on so it's not very hygenic."

3. It's surprisingly expensive! It'll take about 50 pounds of meat to cover you, costing you $250 or more.

4. You will be very cold, as there is "no insulating value at all," one of the butchers says.

5. You will be even colder when your whole costume falls apart. Another of the butchers remarks, "Beyond the sanitary aspects, there's the question of connective tissue. I mean, if you're sewing something like this together there's a very good possibility it's going to split through the grain and fall apart."

Luckily, you still have about a week and a half to think of a non-gross costume idea -- our friends at TODAY have a handy costume guide ready to go.

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