The artist as a fiddler crab
Fiddler crabs are easily recognized by their distinctively asymmetric claws. The movement of the smaller claw from ground to mouth during feeding inspired the crabs' common name; it appears as if the animal is playing the larger claw like a fiddle.
The crab's smaller claw picks up a chunk of sediment and brings it to the mouth, where its contents are sifted through. After anything edible is salvaged the sediment is replaced in the form of a little ball. The presence of these sediment balls near the entrance to a burrow is a good indication of its occupation.