Ace905 writes "For years the razor-sharp beak that squid use to eat their prey has posed a puzzle to scientists. Squid are soft and fragile, but have a beak as dense as rock and sharp enough to break through hard shells. Scientists have long wondered why the beak doesn't injure the squid itself as is uses it. New research has just been published in the the journal Science that explains the phenomenon. One of the researchers described the squid beak as 'like placing an X-Acto blade in a block of fairly firm Jell-O and then trying to use it to chop celery.' Careful examination shows that the beak is formed in a gradient of density, becoming harder towards the tip end. Understanding how to make such hardness gradients could revolutionize engineering anywhere that 'interfaces between soft and hard materials [are required].' One of the first applications researchers envision is prosthetic limbs."