Whistling and hissing sounds are also sometimes heard but are poorly understood. Characters could also be seen whistling or humming tunes at certain points. "Whistle" is an electropop song characterized by a whistling melody. It is a gregarious species, continuously chattering with a range of whistling and squawking calls. Less frequently, various whistling or trilling calls are uttered. Whistled languages use whistling to emulate speech and facilitate communication. It is generally quiet except for some twittering, tweeting, and whistling communication sounds. The song features whistling and sounds of waves crashing on a shore. The sounds are a mix of organ, massed choir, banjo, whistling, and yodeling. Actually, I'm sure that I once heard a bird whistling it as well. We hadn't much breath left for whistling. Cass did her own whistling, which is heard before the song's fade. Harpo used speech on screen, as opposed to other vocalizations such as whistling or sneezing. The wing bar is unique among whistling ducks. At another, Johnny is whistling the waltz.