No matter how you slice it, nine months seems like an awful long time to spend cooped up in the womb, even if it is "biologically essential" or "how mammals work." We already know that fetuses kick, stretch, swallow, and even hiccup to pass the time, but sometimes they've just got to yawn.
In the 1870s, something very strange happened to the French-Canadians working as lumberjacks in Northern Maine. When startled, they would jump in the air, imitate those around them, and even obey random commands. This was the Jumping Frenchmen of Maine disorder.