A few bits of wood chips are not a problem a lot can be in rare cases (I mean a lot) There is a word of caution my vet, VPI and a handful of others all say that one thing that is not digestible is a sheet of paper towel. rats are sometimes wet and paper towel can and has in the past stuck to prey items and been ingested too, that is especially a concern with small snakes. Use plastic or regular paper (doesn't fold and stick the same way) instead as a guard. It simply is not worth taking a chance even if it is slight. There is a member here whom had this happen I just don't remember whom now.