It's a mental disorder.
I'm not making this up.
Imagine going to see a psychologist, and discovering that you have the Jumping Frenchmen of Maine.
You'll probably be quite startled to hear that.
The disorder has more normal-sounding names, such as "latah" and "myriachit" (I take that back. Now that I've written them down they don't sound too normal either).
Anyway, the main symptom of this rare disorder is an unusually extreme startle reaction to unexpected stimuli.
By "extreme" I mean that the patients flail their arms, weep, gasp for breath and become agitated.
The disorder was first identified in Maine and the Canadian province of Quebec in lumberjacks of French Canadian descent, hence the name.
Its origins are supposed to be genetic, possibly influenced by cultural factors. There is no cure, but symptoms improve with age.
I know I know that this piece of useless information will become lodged in my mind forever, taking up valuabe neurons. So it goes.