Yes, as stated, thawing too quickly. I thaw mine in warm, not hot, water for about 45 min and then warm them up with a blow dryer.

Also, sometimes the snake just squeezes extra hard and it happens. It really doesn't bother them any. My girl recently attacked her dinner four times over 20 minutes until it was covered in blood before she ate it. No apparent reason, never done it before, just went insane one night. If she went for it one more time, the belly would have burst and I would have been swearing at her.