The parts of a crab that are inedible include the shell, lungs and stomach. Depending on the species of crab, the claws or innards may also be inedible.
Stone crab and Alaska king crab are two examples of crab species that have few edible parts. Only the claw meat is edible on the stone crab, while the claw meat and leg meat are edible on the Alaska king crab. In both cases, the bodies are discarded. Dungeness crabs and blue crabs have both edible claws and bodies.
The lungs and stomach of a crab are not poisonous to humans, but they taste bad and are not digestible. Crabs are cooked while still alive because dead crabs have bacteria that make them dangerous to eat.