A teacher was taking his class of 12 year olds, and he asks them "Can anyone tell me what part of the body increases to 10 times it's normal size when stimulated?"

There is silence from the class, so he asks the question again. One little girl called Mary stands up and says "You shouldn't be asking questions like that to your class. I think it's very horrible and I'm telling my parents who will tell the head master and he will have you fired!"

The teacher ignores her out burst and carries on, "Can anyone tell me the answer?"

One boy, timmy, raises his hand and says "the part of the body that increases to 10 times it size when stimulated is the pupil of the eye."

"Very good Timmy" the teacher replies. He then turns to Mary and says "I only have three things to say to you young lady. One, you have a dirty mind. Two, if you did your homework you would have known the answer, and Three, one day you're going to be very very dissapointed."