From BBC News:
Snails with left-handed shells can have a big advantage in life – predators may find it impossible to eat them. That is the conclusion of research just published in the Royal Society’s journal Biology Letters. Scientists from the US examined whelks and cone shells preyed on by the crab Calappa flammea. They found the crab is unable to open left-handed shells because it only has a tool for peeling t hem on its right claw; so it discards them. “The crabs have a special tool on their claw, a tooth that’s used like a can-opener,” said Gregory Dietl from Yale University. “So, if you imagine trying to use a right-handed can-opener with your left hand – it’s very hard to do,” he told the BBC News website.