MM explains the findings: the males have one claw which is really large and they use it to attract mates and fight off their rivals. Now when these crabs fight over a love interest, sometimes a male crab will lose this big claw. They have the ability to regenerate these claws but researchers have found that sometimes the regenerated claw is just a dummy, it's grown back but there's nothing really thereï¿½the crab doesn't have any strength in it. But they'll still show it to other males and bluff with it. So it's an interesting example of animals bluffing. (Do the crabs have a choice of whether they will that big claw?) It's lighter, it's toothless and it's not effective as a fighting tool. They don't have a choice in it, it's something that's evolved across generations. But the defense mechanism works for them honestly. (What makes this dishonest? It sounds like the crab is an unwitting benefactor of this evolved gene?) In some respects they are, but they are bluffing and they are getting away with it. Scientists are interested in this because this kind of deception in animals is so rare.