Fainting Goats (as they are called) have a condition called myotonia congenita that makes their muscles get stiff whenever they are startled or excited so they appear to faint. What you really want to check out is the link to the news report on the goats.
“As strange as this may sound, these little critters have actually served an historical purpose. Shepherds often kept the goats in with their flocks as insurance in case of predator attacks. The theory went something like this- as wolves would come down from the hills to attack a flock of sheep, the goats would become startled and, as per the name of their breed, they would faint. The sheep would make a clean getaway, as the wolves would focus on the stunned goats rather than pursue the fleeing sheep. Not that wonderful if you were one of the goats, sure, but downright dandy if you happened to be a sheep. ”