most of us on here, including myself, feed in the cage directly. some people feed in a separate container, whichever works for you and your snake. if you're worried about swallowing substrate i reccomend you switch to peat moss/eco earth. it's brown and in the shape of a brick and can be afound at local pet stores and some gardening stores. it's a little messy and work to take apart, but should your snake swallow it it'll easily pass through with no problem. as for the aspen, if it was a small piece then there shouldn't be a problem unless it was a big chunk or if it was multiple pieces.