You cast your gaze around the room but to no avail, there is nothing you can use to jimmy the lock. It's a bare cell with little more than moss and lichen to accompany you...
...and the crab.
Of course! You pick up the crab, carefully avoiding it's claws and hold it up to the lock. Perhaps if you jig it a bit you could use it's claw as a lockpick. It's a stupid idea but it's all you've got. The crab just stares up with you and you somehow get a sense of exasperation, though it doesn't struggle.
You feel a little stupid, it would be easier to just rip the crab apart and use it's claws yourself, but you don't want to hurt the little thing. Instead, you try to get across what you want it to do, motioning toward the lock and pushing the crab forwards in your cupped hands.
The crab seems to get the idea and begins to work at the lock, all the while shaking it's eyestalks in what you are sure is frustration. After several minutes bent awkwardly, holding the crab up against the lock you hear a click. The crab removes a claw from the lock and looks at you expectantly.
Was it the lock that clicked or something on the other side?