A platypus' nostrils are located on top of its bill, allowing it to breathe when swimming at the surface. It may rest underwater for as long as ten minutes, but can only stay underwater for two minutes when swimming. Young platypuses have poorly developed molars. As they mature, their teeth fall out and are replaced by hard horny pads on the upper and lower jaws. The pads grind food in place of teeth.
Platypuses have keen sight and hearing on dry land.
But the eyes and ears are situated in a furrow which covers them when they submerge in water. It is equipped with sensors that can detect movement in water. Water reaches the sensitive nerve endings through tiny pores in the snout's hairless leathery skin, which is moist and soft. A lesser known platypus curiosity is located on the inside of each hind leg. It is a hard spur that disappears on females as they mature.