"A fainting goat is a breed of domestic goat whose muscles freeze for roughly 10 seconds when the goat is startled. Though painless, this generally results in the animal collapsing on its side. The characteristic is caused by a hereditary genetic disorder called myotonia congenita. When startled, younger goats will stiffen and fall over. Older goats learn to spread their legs or lean against something when startled, and often they continue to run about in an awkward, stiff-legged shuffle.
The origin of the fainting goat is peculiar. The goats appear to have arrived in Marshall County, Tennessee in the early 1800s, courtesy of a reclusive farm worker named Jon Tinsley who was most likely from Nova Scotia. Before he left the area, he sold his goats — three does and a buck — to Dr. H.H. Mayberry, who bred them."
They're bred generally as meat goats, but also make good pets, living from 12-15 years. Apparently in the past they were used for protecting livestock such as sheep by involuntarily "sacrificing themselves" to predators, allowing the sheep to escape. Which is sad for the goats, but also smart.
Every October in Marshall County, the Fainting Goat Festival is held. It's obviously centered around fainting goats, and I can only imagine that it involves vast amounts of goat-scaring and hilarity.