Erm, are you talking about a snake? I read "Ever since I bought him he's has eaten like a pig (even during shedding)." So the shedding part makes me think your talking about a python or something lol.

Anyway if its a frog....you must have an african bullfrog or a big female pacman for it to be able to eat small rats. And I lol at the above post saying it should only eat crickets...

Make sure the temps are around 80 F and that its moist enough, wait another week and try again. If he still doesn't eat, try another type of food, sometimes they get sick of one type of food. That usually works for my frog.