i dont know if it is normal im no ball python expert but my carpets do it alot also. i would assume they strike the thickest part of the body so they could coil it. also do liek i do take a ziplock bag and put your rats in it then set it in your sink in hot water. i do that and have no problems. once thawed i let them set a little longer in it to make the rats bodys warm and my snakes strike immediately on them. the extra warmth makes them thing they are live .