it's my life

A teacher puts a photograph of a Tomcat on the blackboard, and proceeds to ask the class, if they can tell her how the tail is attached to the cat?
Little Mary has the first attempt and answers "By fur Miss?"
The teacher replies "Not quite right Mary, but a good try."
Meanwhile all during the lesson Little Johnny is sitting down the back raising his hand in the air saying "Me, Miss! Me, Miss!"
The next student the teacher picks is Peter, and he answers "Is it attached by skin Miss?"
The teacher replies. "Not quite right either, Peter, anybody else want to try?"
Finally, the teacher had no choice but to pick Little Johnny. She said to Johnny "What do you think the tail is attached by?"
Johnny replied, "Judging by the size of those nuts on the cat I'd say it would have to be bolted on!"