The racket might sound like really loud sci-fi lasers, but listen again: It's the gibbons at the Denver Zoo making that noise. They're singing.

A filmmaker recently captured the piercing noises that were ringing out over the fence from the Denver Zoo.

Intrigued, he inquired on Twitter as to what the sound is/was.

Denver Zoo responded, letting him (and us) know that it's the gibbons within the zoo and their 'song.'

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