These crustaceans can scare off predators even when their usual armour turns soft. Many arthropods are able to produce pulsed sounds by rubbing a hard pick over stiff macroscopic ridges1, rather like dragging a stick over a washboard. Spiny lobsters (Palinuridae) also make pulsed sounds, and here I show that they generate these by virtue of a frictional 'stick-and-slip' mechanism that is more usually associated with bowed stringed instruments. By using this technique rather than a 'hard-washboard' mechanism, lobsters can produce strident warning sounds against predators throughout their moult cycle, including the period when their exoskeleton is softened and they are most susceptible to predation.