Expandable human organ

The male teacher in a girls' school asked the science class: "Who can tell me what organ of the human body expands to 10 times its usual size when stimulated? Mary, can you tell me?"

Mary blushed furiously as she stood up. Then replied, "Sir, how dare you ask such a question? I will complain to my parents, who will complain to the principal."

The male teacher was taken aback at first by Mary's reaction. Then, as understanding dawned on him, he called for another pupil, this time a volunteer.

Lilly put up her hand. "Yes, Lilly?" asked the teacher.

"Sir, the correct answer is the iris of the eye."

"Very good. Thanks, Lilly," said the male teacher.

He then turned to the 1st girl, who threatened to complain to her parents and principal: "Well, Mary, I have 3 things to tell you:

First, you have NOT done your HOMEWORK.

Second, you have a DIRTY mind.

And thirdly, I fear, one day in future, you are going to be sadly disappointed.(bcoz no other part expand to 10 times of its usual size)"