The above image shows a female and 2 male Blue-winged Teals in an atypical situation. They are walking on a mudflat while filtering breakfast out of the mud with their beaks. (Note the female has a bit of the blue patch on her upper wing visible. This confirms her as a Blue-winged Teal and not some other duck who happens to be hanging out with the 2 males.)
The second image shows the two males continuing to plow through the mud and muck filtering as they go. The beaks of the Anatinae have parallel ridges on the underside of the upper beak that are arranged to form a comb-like filter. They use the lower beak to push the syrupy mud through the filter and capture the plant or animal material they consume as food.
The third image shows a single male Blue-winged Teal as he is vigorously squirting mud from the side of his beak. Also take note of the “furrows” in the mud above and below him. Normally, the dabbling ducks are floating above their food source and we don’t get to see the filtering process since it takes place under water. What a way to make a living!