I've noticed this by Bojado and Manny as well as others that either while they walk out or once they are in the ring, they will open their jaw really wide in afew repetitions. Is this to loosen it up to take a hard shot or what? I'm interested to know what makes a boxer do the things he does :D

i think its just to loosen it....its like stretching your muscles so that you dont pull anything

So they won't cut easily...
Makes the skin on their face nice and loose...

just a natural tendency...just like sticking your arms out to stretch...more so to loosen up since they know they will be taking punches on the jaw

It's also to do with tightness in the trapezius muscles. Boxers do neck exercises to strengthen their neck. This leads to an increase in muscle mass, and hence more muscle to constrict. This can effect up into the jaw area, hence the stretching.

Lol :D