I mean... Have you seen/dissected owl feces? It's... interesting looking. A Griffin is a pretty mystical being, so what isn't to say it's like that? Corin DID bite the dog in half in one go, after all.
Edit 2: I just realized that I had the mistaken impression of owl feces. I forgot that owl pellets are actually like cat hairballs in that they're regurgitated. The hairy, bone filled gobbet of slime and stuff is what can't be digested... Big mistake on my part, lol.