American researchers believe they've recorded spontaneous mimicry of the human voice by a Beluga whale.
While other marine mammals have been taught to mimic human speech, scientists say this particular whale appeared to copy human voices deliberately and unprompted.
But the BBC reports researchers have heard a whale named NOC, aged nine, make sounds octaves below normal, in clipped bursts.
They have outlined in Current Biology just how NOC did it.
But the first mystery was figuring out where the sound was coming from.
Belgua whales are known as "canaries of the sea" for their high-pitched chirps, and while a number of anecdotal reports of whales making human-like speech, none had ever been recorded.
When a diver at the National Marine Mammal Foundation in California surfaced saying, "Who told me to get out?" the researchers there knew they had another example on their hands.
Once they identified NOC as the culprit, they recorded his behaviour.
They found that vocal bursts averaged about three per second, with pauses reminiscent of human speech.
Analysis of the recordings showed that the frequencies within them were spread out into "harmonics" in a way very unlike whales' normal vocalisations and more like those of humans.
They then rewarded NOC for the speech-like sounds to teach him to make them on command and fitted him with a pressure transducer within his nasal cavity, where sounds are produced, to monitor just what was going on.
The BBC reports they found that he was able to rapidly change the pressure within his nasal cavity to produce the sounds.
To amplify the comparatively low-frequency parts of the vocalisations, he over-inflated what is known at the vestibular sac in his blowhole - which normally acts to stop water entering the lungs.
In short, the mimicry was no easy task for NOC.
"Our observations suggest that the whale had to modify its vocal mechanics in order to make the speech-like sounds," said National Marine Mammal Foundation president Sam Ridgway.
"The sounds we heard were clearly an example of vocal learning by the white whale."
