Well, I'm not exactly sure. I am no biologist. According to the wikipedia page on chicken hypnotism
, this is a similar phenomenon to a deer freezing when hit by a strong beam of light; it's an attempt to avoid a predator by pretending to be dead. I suspect that's right, chickens are both extremely stupid and very skittish, so this sort of massive overreaction just seems in line with my (admittedly limited) experience with chickens.