1.) They yawn to excercise jaw muscles... especially common right before and after a feeding and very normal
2.) Not sure... good question. I'd be interested in the answer myself.
3.) The snake will not hold on unless it's a feeding response - fear strikes are quick release. Here's a Louisiana method my gramps used at his snake farm for the stubborn ones... put a cloth over its eyes to calm it down, place your middle through pinky fingers behind the snakes head and wrap them completely around his neck (allows future control of snake head to prevent further bites)... hold firmly but don't constrict the snakes neck. Take your thumb and index fingers and place them on either side of the snakes jaw behind the eyes. Apply soft pressure... if there isn't a release then dip snake's head under warm water. (This method is not intended for venomous snakes)
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-Iman
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Hope it helps...