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

Genetic disorder

A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....

 called myotonia congenita

Myotonia congenita

Congenital myotonia is a genetic, neuromuscular channelopathy that affects skeletal muscles . It is congenital, meaning that it is present from birth. Amongst other problems, it causes delayed relaxation of the muscles and rigidity...

. 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.
Slightly smaller than standard breeds of goat, fainting goats are generally 43 centimetre tall and can weigh anywhere from 27 kilogram.