Some seem to not care, mine won't even try. He constricts all of his food for 3-ish minutes even though he's on f/t and sometimes he'll unwrap, forget where the head is, stare at the butt for a couple minutes and decide "no, that smells like crap", and then frantically look for the head. One time he was completely perplexed and practically breaded the mouse with the eco-earth so I tossed that one, thawed another, and stuck it on a paper plate for him and he took that without issue. I actually ditched the substrate and switched to paper towels because of that.