A farmer had a brown cow and a white cow, and he wanted to get them bred, so he borrowed his neighbor's bull and turned it loose in the pasture.

He told his son to watch and tell him when the bull was finished.

After a while the boy came into the living room where his father was talking to some friends.

"Say, Pop", said the boy.
"Yes", replied the father.
"The bull has just screwed the brown cow!".

There was a sudden silence in the conversation. The father asked his friends to excuse him for a moment, took his son outside and said:
"Son, you musn't use language like that, especially in front of company. You should say that the bull 'surprised' the cow. now go and watch and tell me when the bull 'surprises' the white cow".

The father went back inside the house.
After a while the boy came back and said "Hey, Daddy!".
"Yes, son, did the bull 'surprise' the white cow"?

"He sure did, Pop! he screwed the brown cow again!"