I feed my snake in his enclosure, and since the rat is wet from the hot water he gets a little aspen in his mouth but some bedding in his mouth here and there isn't going to have any ill effects, it just looks like he wants to attack since his mouth will be partially opened from the shavings!But anyway, my snake has bit me, I am not saying this is from cage aggression, its just me not reading the signs leading toward a bite(then again, it does not hurt, so its alright).
Do you feed F/T or Live?
If you'd like to prevent your snake from eating your substrat, just put a piece of paper down before you put the prey in.