Anatomy

During a human science class for younger students, the teacher
asked the students what part of the human body could grow to six
times its size at certain times. A little girl raised her hand
and said, "Teacher, you know my daddy's a preacher and you know
we don't say those words in my house. You are just trying to
embarrass me." Next he called on Johnny and Johnny said, "The
iris, it grows to six times it size when you are in the dark."
Teacher said, "That's right Johnny." Then said, "Little girl you
have a very dirty mind, and when you grow up and get married one
day, you are going to be very disappointed."