African elephants have a grey folded and up to 30 mm (1. 2 in) thick skin that is covered with sparse bristled dark-brown to black hair. Short tactile hair grows on the trunk, which has two finger-like processes on the tip. Their large ears help to reduce body heat; flapping them creates air currents and exposes the ears' inner sides where large blood vessels increase heat loss during hot weather. The trunk is a prehensile elongation of its upper lip and nose. This highly sensitive organ is innervated primarily by the trigeminal nerve, and thought to be manipulated by about 40–60,000 muscles. Because of this muscular structure, the trunk is so strong that elephants can use it for lifting about 3% of their own body weight. They use it for smelling, touching, feeding, drinking, dusting, producing sounds, loading, defending and attacking. Elephants sometimes swim underwater and use their trunks as snorkels.