It was one of the greatest mysteries of the deep blue sea. Migrating whales often turn up with crater-like wounds on their skin but, until now, nobody has ever known why or how the injuries are sustained. The main suspects ranged from barnacles to infection, but two South African scientists - Peter Best and Theoni Photopoulou, from the universities of Pretoria and Cape Town respectively - have finally solved this global mystery.The perpetrators are cookie-cutter sharks which rise from 4km in the depths to a mere 1km below the surface to take a hunk of fresh meat off passing whales.George Burgess, an expert at the University of Florida, said: "They have the biggest teeth of any shark in relation to the size of their jaws."The sharks also rely on disguise. They can produce their own light on parts of their bodies, which causes their victims to mistake them for squid. When larger fish arrive to munch on the squid, the cookie-cutter in turn takes a bite out of the larger fish. ..