I have seen some rats that are sensitive have a nasty, potentially fatal respiratory reaction even to kiln-dried pine or aspen, so there is obviously still a little aromatic oils left. Also, snakes and other herps will eat anything regardless of whether or not they're fed in that enclosure. Have seen lots of photo examples from vets, esp. calcium sand, regular sand, fine gravel, large rocks, and bark. Shavings seem less commonly eaten and I haven't heard of carefresh or pelleted paper being consumed yet, but it could theoretically happen. Some animals aren't so bright. No vets that I've heard from seem to think that newspaper sheets or the cage carpet would be a problem for this reason.