A platypus eats insects, shellfish, larvae and other small animals that it finds along the bottom of the streams and rivers near its home. It uses its bill and small rocks to scoop up these organisms.
According to National Geographic, platypuses use the rocks they pick up to help mash up their prey before swallowing because they do not have teeth. They can stay underwater for a minute or two at a time and are able to sense the electrical fields caused by the movements of their prey, which they use to find the animals underwater. They do not seem to use their other senses for hunting.