possibly old wives tale, but does she have good ventillation? do you handle her? and if yes, does she do it when she is out of her enclosure? i heard yonks and yonks and yonks ago that snakes yawn for a similar reason to ppl, which is to do with the balance of oxygen to carbon dioxide and the movement of air. please someone correct me on this if i am in the wrong ball park i hate basing care on speculation.