The bird's usual cry is a low, guttural croak. The female frog will not "chirp" or "croak" as often as males, but do sometimes. The adult also rarely emits a low croak, while young frequently squeal. Young birds have been heard making a hissing croak in flight. The croak of the American bullfrog ("Rana catesbiana") is sometimes written as "jug o' rum". The call is a loud heron-like croak. Frogs croak at night, which can keep people awake at night. Displaying males croak and produce a strange deep humming. Rabbitt's second album, "A Croak and a Grunt in the Night", was released in 1977. "Kero" means "frog's croak" and "Hasunoe" means on a "lily pad". It has a croak like the other raven species but with a more whispering note. The peasant pretended that the hide was a soothsayer and made the raven croak. When alarmed, the secretarybird may emit a high-pitched croak. The knob-billed duck is silent except for a low croak when flushed. The call or croak of a frog is unique to its species.