(This one's slightly morbid, folks.)
I'd always heard the phrase "running around like a chicken with its head cut off" as a kid (mainly used in reference to something I was doing at the time, but we'll leave that unexplored for now). I never really understood this until I learned from a girlfriend who grew up on a farm (who was actually my future wife, but we'll leave that unexplored for now) that when you "process" a chicken -- i.e., send it on its journey from pecking at seeds to the KFC bucket -- you first behead the bird, at which point it flops around wildly until expiring.
On some level, I guess I always wondered why the body should behave in such a way, and it turns out that many of a chicken's activities are actually controlled not by the poultry's brain but by its brainstem, so the bird is actually still "alive" in its headless state until it bleeds out. Fair enough -- but this raises the possibility that if the beheading isn't executed quite correctly, the headless chicken can survive for quite some time. Months, even. It will continue to "peck" at the ground and stamp its feet and, generally, act "chicken-like".
But hey, don't take my word for it.