That may be an entirely different animal(haha!) figuratively literally.I use naturally shed dungeness shells. They wash up on the beaches year round, here. Sometimes the chickens get to them before I've even had a chance to wash them off (mischievous Barred Rocks), and they can peck them apart. They also get whatever oyster shells that the racoons and ravens drop around the property. I throw them on the driveway to get crushed. I very rarely have to pay for my flocks calcium.
The lobster shells, especially legs and claws, and snow and king crab legs I've had are very thick, hard and sharp.
Have cut my hands on them more than once, no way I'd give them to the chooks.
Guess you've got to use some discretion and common sense.