One day, Moshe is walking past the wooden fence at the side of the local mental care home when he hears the residents inside chanting, “Thirteen! Thirteen! Thirteen!”
Moshe is quite a curious kind of man and wonders whether a Bar Mitzvah is taking place. So he searches for a suitable hole in the fence and then he looks in. But immediately, someone inside pokes him in the eye with their finger.
Then the chanting begins again, “Fourteen! Fourteen! Fourteen!”
From Oy! The Ultimate Book of Jewish Jokes, by David Minkoff