While dolphins have been taught to mimic the pattern and durations of sounds in human speech, no animal has spontaneously tried such mimicry.
But researchers heard a nine-year-old whale named NOC make sounds octaves below normal, in clipped bursts.
The researchers outline in Current Biology just how NOC did it.
The first mystery, though, was figuring out where the sound was coming from.
The whales are known as "canaries of the sea" for their high-pitched chirps, but while a number of anecdotal reports have described whales making human-like speech, none had ever been recorded.
Once they identified NOC as the culprit, they caught it on tape (view video below) ( via bbc.co.uk ).