A man leaves his house every morning to walk to work and passes a mental hospital surrounded by a wooden fence. Every morning the patients are out in the yard and he can hear them saying in unison,
"10, 10, 10, 10, 10".
One day, he gets curious and looks through a hole in the fence.
Suddenly, a knife shoots out and stabs him in the chest. He falls down and something crawled out of the drain, dragging the body down.
Later, someone else walked by and they can hear the patients saying,
"11, 11, 11, 11, 11"