This is so bizarre that when I first saw the video below, I thought it was an April Fool's joke. These so-called "fainting goats" stiffen up and fall over when startled. I thought, "there's no way that could possibly be real." But after doing some quick research into it, I discovered that sure enough, this is a real breed of goat and its "fainting" is a real condition.
It's a great example of a genetic trait that shows up in domestic animals that would never be found in a wild population. Imagine a wild goat that fell over when a predator attacked. It certainly wouldn't live long enough to reproduce and pass the trait on to the next generation!