Early spring season, at dawn, in the grassland of the western US, the Greater Sage Grouses gather at a lek to look for the perfect mates. To win the heart of the females, along with making the strutting display, the males make a series of sounds noticeable by a couple of low booming pops from two air sacs normally hidden behind the neck pouch. To inflate the air sacs, the males try really hard to maximize the intake for more air. In doing so, at a correct viewpoint, their heads sometimes become invisible.