I used to give mine eggs, but I cracked it for himLike I mentioned before, they like snails and eggs to eat too. Ive heard they also eat frogs but thats a bit cruel to the frog.
Im not sure if i would risk feeding him snails from your garden but you should try giving him an egg, it looks freaky as they get the whole thing in their mouth then crush it. Probably start with a smaller sized egg so theres no choking risk, its pretty messy so maybe do it on a day you plan on cleaning up the cage.