The whale has nerves to its mouth and tongue that can stretch to double their normal length, then snap back without damage, said Wayne Vogl, a professor in the department of cellular and physiological sciences at UBC.
"The nerves that supply these remarkably expandable tissues in the floor of the mouth of rorqual whales ... are very stretchy, they're like bungee cords,"
It was a surprising discovery, as most vertebrate nerves are more of a fixed length, said Vogl.
Whale expands from mouth to 'belly button'
The rorqual whale, which can grow to more than 20 metres and weigh several tonnes, feeds on schools of krill or small fish by opening its huge mouth and letting in a large amount of water, along with the food.
That volume of water can be larger than the whale itself, said Vogl, as the whale's mouth expands all the way to its "belly button."
Vogl and colleagues had been focused on the muscle and blubber of the whale's mouth, when one of the researchers picked up a thick white cord that was really stretchy.
Upon further inspection, the team realized it was a nerve.
Nerves fold and unfold to avoid damage
With a mouth that "basically expands like a balloon," it makes sense that "all the wiring and plumbing" would have to expand too, said Vogl.
But researchers didn't know how the nerves could reach such length without breaking.
It turns out the nerve fibers themselves aren't stretching at all — but folding and unfolding within a protective layer of tissue.
"So the nerves themselves aren't actually hurt or injured by the stretch."
The researchers obtained the whale specimen from commercial harvesters in Iceland, one of the few countries in the world that still practises commercial whaling.