If you happen across a pond full of croaking green frogs, listen carefully. Some of them may be lying. A croak is how male green frogs tell other frogs how big they are. The bigger the male, the deeper the croak. The sound of a big male is enough to scare off other males from challenging him for his territory.
While most croaks are honest, some are not. Some small males lower their voices to make themselves sound bigger. Their big-bodied croaks intimidate frogs that would beat them in a fair fight.