Another joke I've always liked, for some reason

A man was walking down a sidewalk past a high plank fence around the local insane asylum. As he hears a low, rhythmic chanting, apparently from the poor souls on the other side of the fence. About twenty feet ahead, he sees  a knothole, the only one for the hundred yards or so of fence he's passed. As he gets closer to it, the chanting gets louder and more clear. "Fifteen, fifteen, fifteen ..,"

He decides to see what those poor insane loonies are up to. When he gets to the hole, he bends over and peers into it, but sees nothing but a long finger with a sharp, jagged nail hurtling at him. A moment later he feels a terrible pain and falls back screaming as his eye is poked out. Through his own screaming, the man hears the chanting, slightly different.

"Sixteen, sixteen, sixteen ..."

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I don't know why, but I've liked that since the first time I heard it. Admittedly, I wrote it down to be creepier than when it's told, but it's still one of the most horrible things I've ever heard. It's only funny in the darkest and most macabre way, but I always laugh.