(This is an original style shaggy dog story. You have been warned (Alan).
From: JOKE-OF-THE-DAY [RateJoke@JOKE-OF-THE-DAY.com]

Woody Allen was asked his favorite joke. The following is his response:

A man buys a horse from an old man.

The old man says, “The only catch is that this horse loves sitting on watermelons. If he sees a watermelon, he is going to sit on it.” The man says OK. As he’s riding his horse, he comes along a stream.

The horse stops in midstream and sits down. The man beats the horse, but the horse refuses to budge. The man pushes and shoves the horse, but the horse refuses to move.

Finally the man drags the horse out of the river and brings him back to the old man.

“I don’t understand,” the man says. “He sat down in the middle of the river and refused to budge. You told me he likes to sit on watermelons, so I don’t understand why he was sitting in the middle of the river.”

“I forgot to tell you,” the old man replied, “he also likes to sit on fish.”