13
 

A man walks past a big wooden fence in front of the insane asylum and hears all the residents inside chanting, "Thirteen! Thirteen! Thirteen!" in unison.

Quite curious about this, he finds a hole in the fence, and looks in.

Immediately, someone on the inside pokes him in the eye.

Before the man could even react to the eye-poking, the people on the other side of the fence begin a monotone chant of...

"Fourteen! Fourteen! Fourteen!"