What part of the human body increases to 10 times it's normal size when excited?

Question

First person to answer correctly recieves 10 points (the best answer for this question)

Answer 1

lets get together and find out ;)

Answer 2

that's a HARD one

Answer 3

That's easy...the pupil of the eye

Answer 4

Isn't that the pupil of the eye?

Answer 5

The pupil,