It was a tale of two tongues when Darwin resident Liam Mercer stumbled upon the slimy remains of two whales on the shores of Casuarina Beach on Friday.

Dispersed across 200 metres, the find "looked fresh".

"If you look closely, you can see the arteries and blood vessels where they've been chopped off," he said.

"They were maybe 30 or 40 centimetres long and one of them looked fairly clean cut.

"The mystery is, what were they and how did they end up there? It's certainly got tongues wagging, that's for sure."

According to Carol Palmer, a marine mammal expert with the Department of Environment and Natural Resources (DENR), the gruesome discoveries have been confirmed as whale tongues.

Whale expert Dr Carol Palmer believes an orca could be behind the attack. ( Supplied: Liam Mercer )

But from just what whale — and the identity of their killer — remains a mystery.

The running theory is an orca attack. The species is known to prey on humpback whale calves, and despite popular belief, the Top End is in fact home to tropical killer whales.

"Killer whales are pretty good at eating humpback whale calves, and the thing they love the most is their tongue," Dr Palmer said.

"It's the time of year when the humpback whales are here and calving, so it kind of makes sense on some level.

"But it's kind of interesting to then have the tongues roll up, [which] makes me think twice about [that theory]."

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Alternatively, researchers believe the tongues could have come from a Bryde's whale or 'false killer whale' — smaller animals known to inhabit the waters of northern Australia.

But without a corpse — or a sample — it's hard to definitively say.

"The size of the tongues, they're definitely from a small whale," Dr Palmer said.

"The Bryde's whale, which is about 10-12 metres, they're a pretty shy kind of whale … [but] have been [sighted] off Arnhem Land, not Darwin.

"Or potentially it is a false killer whale and they've just ended up in some sort of situation."

Killer whales are known to prey on humpback calves to claim their meaty prize ( Supplied: Liam Mercer )

So who's the elusive killer?

Though an orca may have been responsible for the initial attack, Dr Palmer said it "didn't add up" that the species would leave its meaty prize behind.

"Maybe the calves actually were dead or had been attacked, something moved the killer whales on and the crocodiles came in," she said.

"We regularly get crocodiles munching away at green turtles, they're such a tough animal … so maybe they ate away and the tongues floated off.

"It could be sharks, it could be killer whales or it could be crocodiles."

For now, it's a mystery Darwinities will be left to chew on.