picture of the day on the Wikipedia home page is this splendid picture of a flesh-fly:
Flesh fly, from the Sarcophagidae family "blowing a bubble". One explanation for this behaviour is that it concentrates the fly's meal by evaporation. The diet of the flesh fly is very high in water content. The fly regurgitates the liquid portion of the food, holds it whilst evaporation reduces the water content and the fly then swallows a much more concentrated food meal without the water content. This continues until sufficient amount of liquid is left for the fly.