There is a very interesting breed of goats called the Fainting Goat. These goats suffer a genetic condition called myotonia congenita, which produces fascinating yet hilarious situations. When startled by the sudden presence of another animal or even a loud noise, these goats all suddenly freeze and fall to one side. This phenomenon can occur even while running, which causes the goats to crash into the ground, lying on their backs with their legs straight up. This can even occur from the excitement of seeing food and starting to run towards it.
The reason for this peculiar phenomenon is that myotonia congenita damages systems that allow muscles to relax, causing it to become easily excited. Ergo, when a goat is startled, its muscles tense reflexively, causing it to contract suddenly while taking longer to relax. This results in the goat becoming paralysed and falling. Young goats tend to be helpless when this occurs, but more experienced goats prop their legs apart quickly or lean against something to prevent falling (they can even be seen hopping on their stiff legs). These “fainting spells” are painless.
Although this kind of trait is often removed by natural selection (for example, in nature these goats would freeze when they meet a predator, and then proceed to be eaten), humans have bred these goats specifically to save their trait. In old times, these goats were used as “sacrifices” so that they would get eaten first when wolves struck, but nowadays they are bred in certain farms for no particular use.
Myotonia congenita also affects other animals such as cats, and there are many people in the world affected by this condition too.