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 transplantsgone 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." Find The Body Odd on Twitter and on Facebook.