For centuries, people have debated whether a human head will continue to think, sense, or even try to talk after it's been severed from the body... and if so, for how long? Witnesses to decapitations have claimed that the victims' eyes blink and look around, their faces show terror or pain, and their mouths form words.
Those macabre accounts are so well-known that fully aware noggins are practically a horror cliché by now, and movies like Re-Animator take the idea to the ultimate extreme (and we love it for that, of course). One of the most chilling monologues in horror cinema comes from Brad Dourif as the Gemini Killer in The Exorcist III, wherein he claims a severed head can see for up to twenty seconds, and describes what it's like to position his victim's head so they can see his handiwork.
But are the tales that inspired these movies just the product of shocked onlookers misinterpreting a simple muscular reflex? Most doctors would say yes – decapitation should result in an instant coma from shock and loss of oxygen, even if brain-death takes longer, and lower brain functions can cause facial reactions even when the higher brain functions are shut off. But in a recent study cited in LiveScience.com, at least one group of researchers thinks otherwise.
An experiment conducted by Dutch scientists showed that electrical activity continued in the brains of mice up to four seconds after decapitation (we know what you're thinking, and we're not condoning this, just reporting it), and theorized that the duration could be even longer for mammals with larger and more complex brains – in other words, humans. So maybe the Gemini was right, and a beheaded victim could be quite aware of their final horrifying moments.
Just pray you never find out for yourself...