In the late 1980s, staff at the National Marine Mammal Foundation in San Diego, California heard what they thought was the sound of human conversation. They were surprised and delighted when they discovered that the noise was coming from a beluga whale called Noc.
Scientists' fascination with the case has been rekindled by the journal Current Biology, which has published new insights on the story, and posted audio on the internet of the whale in "conversation" mode.
While birds have been known to mimic human speech, it's not a common characteristic among mammals - the few exceptions apparently including Noc and, a decade earlier, a New England harbour seal named Hoover, who reportedly spoke with a Maine accent.
Although marine biologists have confirmed the phenomenon, they don't claim that the animals were attempting communication. But it's an area of research that holds out hope for further understanding of other species.
Noc lived until 2007, but he stopped making human-like sounds after four years, possibly because he had reached sexual maturity. Or perhaps he simply realised there was nothing we humans could tell him that was worthy of a response.