(This is one that was told to me by an American when I was in Germany, 30 years ago)

This man had a great pain in his tummy, so he decided to go and see his Doctor.

The Doctor examined the man's stomach and proclaimed that he had a huge worm therein. It was a monster of a worm!
The Doctor told the man that there was only one way in which to get rid of it, and asked him to come back the next evening at 5 pm and to bring a banana, a hammer and a cookie when he comes.

The man exclaimed, "A banana, a hammer and a cookie?" and the doctor replied, "Yes, a banana, a hammer and a cookie.

The man went away puzzled and came at 5pm the next day with a banana, a hammer and a cookie.

The Doctor took the man into his surgery and asked him to take off his pants and to bend over. He then unpeeled the banana and shoved it up the man's arse and beat it right in with the hammer, started a stop-watch and exactly five minutes later he shoved the cookie up the man's arse. The man, who had rather enjoyed the banana, screamed in pain when the cookie went in.

The Doctor asked the man to come again the next eveningt with a banana and a cookie, but to leave the hammer behind as there was no point carrying it up and down.

When the man came the next day, the procedure was repeated.

This went on for six days by which time the man was absolutely fed up of the strange treatment given to him by the doctor.

On the seventh day which was to be the last day of "treatment" the man was asked to bring only a banana.

"What about the cookie, Doc ?" he asked.

Doc replied, "No, only a banana this time"

As usual the man was asked to strip and bend down. The banana was unpeeled and hammered home. The Doctor took his stop watch and started timing. Five minutes passed, and six minutes passed, and seven minutes passed.

Suddenly, the worm put its head out of the man's arse and shouted, "and where is my fucking cookie?"

The doctor who had the hammer in his hand whacked the worm on the head with it, killing it instantly.