Or the answer is soulely you'll release him. He said he'd eat him but never kill him. He may just take a nibble or om nom nom some of his leg. Like most creatures that are famished they can't eat too much at once or their stomach could react my exploding (more of ripping)
I believe the crocodile is normally vegetarian except in the case of the boy. If he is slim, he would have found plentiful of meat (be it fish, human, or reptilian) however, there is little vegetation near the Nile. The crocodile will only eat the boy if she says he will, and only release him if she says he will. After all, most crocodiles attack on sight, but if he has intelligence than he realizes (like the majority of philosophers) that we decide our own fate and that of those around us.