A man is talking to his friend. "I think my wife is being
unfaithful to me. And I think she's going out with a tennis
player."

The friend asks "Tennis player? Why?"

"Because", answers the other, "I found a racquet under our bed".

The friend thinks for some seconds and says "Gee, I think then
my wife is being unfaithful to me with a horse".

"A horse?? How come? Why??"

"Because I found a jockey under our bed."