I think they do both.
Bo LOVES and I mean LOVES paper. If anything is near him orwithin his reach, he's chewing it. I have found envelopeswith little crescent shapes missing from them, schoolpapers,newspapers, anything!
I know he will eat that, but he doesn't eat cardboard much. I'm sure he eats some of it.
Recently I found a few "adjustments" made to my purse. :X