The way a platypus eats is something humans have only begun to understand. Thanks to world-renowned scientist Henry Burrell, we know a little bit. At least, we know now that they're real! It's just that we don't know a huge amount, mostly due to the fact that you have to be able to withstand very cold water to be able to study them. Burrell actually half-paralyzed himself doing just that.
The duck-billed platypus, he discovered, finds its food by detecting electric currents of prey as it swims underwater. It does this by closing its ears, eyes and nose. Special receptors within find muscle activity. It should be noted that platypuses are the only mammals which are able to do this! This ability is called electro-reception. Other animals with it are sea creatures like sharks and rays. (Dolphins find their prey via sonar, which is very different). However, the receptors that control electro-reception in the bill of the platypus take up a huge amount of its brain. Consequently, platypuses have been fooled by scientists when they send a small electric current into the water.
Since platypuses can survive at temperatures below 41 degrees, they can dive pretty deeply. They will spend a good amount of the day in the water, especially on overcast ones. Searching for food takes up much of their life. In a study by Philip Bethge, platypuses were found to exert more energy than usual during the cold seasons. And in fact, they must do this a lot; in the best of times they can only stay under the water for 40 seconds. Platypuses have a lot of energy for diving, it seems, but not for swimming itself!
Platypuses are completely carnivorous. They generally eat invertebrates, like shrimp or crayfish. One of their favorite foods, however, appears to be a kind of tube worm. This creature is found in large amounts at Salmon Ponds in Southern Tasmania. Consequently, a lot of platypuses tend to live around that region. When hunting, they'll catch as much food as they can at one time, and fill their cheek pouches. They don't come up out of the water till these are full, or until the platypus needs air. But every day, they do need a lot of food; about 20% of their body mass in fact.
They chew with rough patches in their mouths. This is done when they've gotten to the surface with a full amount. They grind their catch to a very small size for digestion. This is all because platypuses actually have no teeth!
We know that since platypuses have a small GI tract, it probably doesn't take long for them to digest food. It has been found that they have a pretty high metabolism. However, platypuses' actual digestive methods have been little examined other than that. People instead rely on what information they can get from the fairly large cheek pouches of the beasts. Basically, then, we know only a little more about the eating habits of the platypus than what Henry Burrell himself discovered decades ago.