"Boy Sees Elephant" joke

Father, mother and son decide to go to the zoo one day. So they set off and are seeing lots of animals. Eventually they end up opposite the elephant house. The boy looks at the elephant, sees its willy points to it and says, "Mummy, what is that long thing?"
His mother replies, "That son, is the elephant's trunk."
"No, at the other end."
"That son is the tail."
"No, mummy, the thing under the elephant."
A short embarrassed silenced after which she replies, "Thats nothing."
The mother goes to buy some ice-cream and the boy, not being satisfied with her answer asks his father the same question. "Daddy, what is that long thing?"
"That's the trunk, son" replies the father.
"No at the other end."
"Oh, that is the tail."
"No, no daddy, the thing below," asks the son in desperation.
"That is the elephants penis. Why do you ask son?"
"Well mummy said it was nothing," says the boy.
Replies the father: "I tell you, I spoil that woman..."