Gestures, eye contact, and voice
Taking blood test weekly too make sure you stay away form HIV
Some one had the same question as you so here is someone answer.
Because it is flexible. Think about it; the ribs protect both the lungs and the heart. If the ribs were solid bone all the way around then unless you constantly break your ribs you wouldn't be able to expand the cheat to breath. Additionally your lungs would constrict the heart to a degree that it would function properly.
I think the answer is the pituitary.
