Bats navigate and find food in the dark using sound. They make about 50 high squeaking noises a second. The sound hits a solid object and the bat's large sensitive ears pick up the echo. They seem to be able to tell the shape of an object by this echo. In an experiment, bats used echo-location to fly through wires 30 cm (12 in) apart in total darkness without hitting them. If a bat's mouth is full it cannot squeak so some use their noses. Folds of skin called 'nose-leaves' around their noses direct sound like megaphones.