Aspen shavings or cypress mulch can be used without incident as a subtrate as long as you take the proper precautions. A big "no no" is feeding in the enclosure when shavings are present, as they can easily get lodged in your snake's mouth. If you have to feed in the enclosure, cover the bottom with something to preven the substrate from getting in the snakes mouth. I prefer not to feed in the enclosure, I feed my Burm in the tub, but the RTB will not eat in the tub, so I have to put something in over the shavings to protect her.
