which organ of the human body expands to 10 times

Sixth grade science teacher Mrs. Samson asks her class: "Who can tell me which organ of the human body expands to 10 times its usual size when stimulated?"

Nobody raises a hand, so she calls on the first student to look her way. "Mary, can you tell me which organ of the human body expands to 10 times its usual size when stimulated?"

Mary stands up, blushing furiously. "How dare you ask such a question?" she says. "I'm going to complain to my parents, who will complain to the principal, who will have you fired!"

Mrs. Sampson is shocked by Mary's reaction, but undaunted. She asks the class the question again, and this time Sam raises his hand.

"Yes, Sam?" says Mrs. Sampson. "Ma'am, the correct answer is the iris of the human eye." "Very good, Sam. Thank you."

Mrs. Sampson then turns to Mary and says, "Mary, I have 3 things to tell you: first, it's clear that you have not done your homework. Second, you have a dirty mind. And third, I fear one day you are going to be sadly disappointed."