Funny Joke: I was walking past an insane asylum and I heard chanting coming from behind the fence

I was walking past the outside of an insane asylum the other day.

As I walked along beside it, I heard chanting coming from behind the fence further up… they were chanting numbers, or rather, just one number.

"Thirteen, thirteen, thirteen, …" they excitedly chanted.

All of them saying the same number over and over.

As I approached I saw a small hole in the fence just big enough to look through.

So, with the crowd continuing to chant "… thirteen, thirteen, thirteen," I leaned down to look in the hole to see what was happening in there.

Just as I put my eye to the hole, a finger poked me in the eye, the crowd cheered loudly, and started chanting again.

"Fourteen, fourteen, fourteen…"