A video shared clip from the BBC’s Spy in the Ocean reveals the other-worldly POV of a robot herring diving into one of nature’s greatest spectacles: a massive school of farting fish. If you’re thinking, “Really, IFLS? Must we talk about farting?” then let me tell you, the unique swim bladder found in herring saw them become a matter of international security not that long ago.

Sweden, Russia, and the farting fish

In 1982, several Swedish submarines, boats, and helicopters went in pursuit of a mysterious underwater signal in a search that would go on for over a decade. In the wake of the Cold War, intrusion by Russian subs was high on the list of concerns, but it would turn out to be herring farts.

“It sounded like someone frying bacon. Like small air bubbles releasing underwater,” said Magnus Wahlberg in a TEDx talk. As a professor at the University of Southern Denmark, Wahlberg became involved in an investigation into the strange signals. 

“It turns out herring have a swim bladder… and this swim bladder is connected to the anal duct of the fish. It’s a very unique connection, only found in herring. So, a herring can squeeze its swim bladder, and that way it can blurt out a small number of bubbles through the anal opening.”

Wahlberg was able to test the theory by purchasing a herring from a store and effectively pressing on its swim bladder. When footage of the experiment was played back to navy personnel, they were convinced it was a match, confirming that Sweden wasn’t under threat from Russia.

Spy herring: into the heart of a gassy beast

Herring gather in their millions, making it easy enough for Spy In The Ocean’s spy herring to slip into the fold. The video reveals a strange sound that’s audible the closer it gets to the herring, and it would no doubt be a familiar sound to anyone onboard a Swedish sub during the great signal search of 1982. Yes, spy herring is hearing the very fish farts that Russia and Sweden nearly came to blows over.

“The clicking is made by the herring,” says narrator David Tennant. “As the schools build so do the clicks. They’re from bubbles squeezed from their swim bladder.”

As the video shows, Swedish officials aren’t the only ones lured in by the sound. Sea lions can be seen hunting the herring, forcing the massive school into shallower waters where they’re easier to pick off. Evidently, it’s not easy being gassy, for humans or fish.