Siamangs are large black gibbons that live in the rainforests of Sumatra and the Malay Peninsula, and they are famous among primates for calls that can carry for kilometres through dense forest. Males and females use the booming hoots to mark territory and stay in contact, with an inflatable throat sac acting as a natural amplifier. Online, short clips of the call circulate as a generic monkey sound, prized because it is instantly recognisable, louder than expected, and funnier than a typical chatter. That combination keeps it popular for reaction edits and animal compilations.