"ELEPHANT'S.......?????" joke

A couple took their young son for his first visit to the circus,
and by chance their seats were next to the elephant pen. When his father left to buy popcorn, the boy piped up, "Mom, what's that long thing on the elephant?"
"That's the elephant's trunk, dear," she replied.
"No, not that."
"Oh, that's the elephant's tail."
"No, Mom. Down underneath."
His mother blushed and said, "Oh, that's nothing."
Pretty soon the father returned, and the mother went off to get
a soda. As soon as she had left the boy repeated his question.
"That's the elephant's trunk, son."
"Dad, I know what an elephant's trunk is. The thing at the other end."
"Oh, that's the elephant's tail."
"No. Down there."
The father took a good look and explained, "That's the elephant's
penis."
"Dad, how come when I asked Mom, she said it was nothing?"
The man took a deep breath and replied, "Son, I've *spoiled* that
woman."