The 6th grade science teacher asked her class, "which body part
 increases to 10 times its size when stimulated?"

 No one answered for a long time till little Mary stood up, angry, and
 said: "the teacher should not be asking 6th graders a question like that! I
 am going to tell my parents, who will tell the principal, who will fire you!"

 The teacher ignored her and asked the question again, "which body
 part increases to 10 times its size when stimulated?"

 Finally Billy stood up and  said that the body part that increases 10
 times its size when stimulated is the pupil of the eye.

 The teacher said "very good,  Billy, "then turned to Mary and said, "As for
 you, young lady, I have three things to say, one: you have a dirty mind.
 Two: you didn't read your homework, and three: one day you will be
 very, very disappointed.