You might hear a variety of unusual sounds while you're underwater, as given the fact that it's not our natural habitat, a lot of noises might come as a surprise.
But one thing you never want to hear while you're below the surface is the piercing 'ping' of an active submarine sonar.
Accidentally subjecting your ears to this sound can not only startle you during a swim, but it can also have dire consequences on your health.
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Unfortunately for this diver, there wasn't much he could do about his unexpected run-in with the sound navigation and ranging technology - but thankfully, he did live to tell the tale.
As well as having an impressive story to share with his mates down the pub, Jean Kikine can also give us all an insight into what impact the experience had on him.
Sonar tech is an incredible bit of kit for exploring deep seas and mapping large bodies of water, and it's come in seriously handy during incidents such as the 2023 search for the Titan sub.
Essentially, active sonar transducers emit acoustic signals or pulses of sound into the water, with the hope that it will hit any objects that may be of interest.
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If there is something in the water, the sound sent out will bounce back off the item and return an 'echo' to the system.
Those on the submarine can then calculate the strength of the signal, and the operators get an idea of what it may be.
Sound is a more reliable tool underneath the surface, as light doesn't travel very well, so most boats are equipped with active sonar technology these days.
If humans run into high levels of active sonar, it can cause dizziness, disorientation, temporary memory issues, concentration problems and temporary hearing loss.
In serious cases, it can even cause organ damage, while a marine bioacoustics scientist previously told the West Australian that active sonar pulses can even rupture the lungs.
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The boffin warned that pings exceeding 210dB can cause fatal brain haemorrhaging - but luckily for Jean, he managed to escape largely unscathed.
Still, the chilling footage he captured of what he believes to be a submarine's active sonar still managed to scare a load of social media users.
After posting the footage, which was shot in the Bahamas, to YouTube in 2019, the diver shared further details of the incident in a Reddit thread.
Jean said he 'understood what [the sound] was immediately', explaining that he was about 60ft below the surface at the time and felt both 'excited and worried'.
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He described the area he was diving in as a 'submarine playground', so perhaps he was anticipating the potential for his 'first ever' run in with sonar - but still, it didn't prepare him for the physical effects he experienced.
Jean told social media users that it was 'very, very loud' and he 'felt the sound in his body' - while adding: "Not painful, but I [can] confirm you feel it entirely with your body."
People were left petrified after watching the clip and flooded the comment section with their thoughts.
One said: "Jesus, it's that loud?"
Another wrote: "That is so haunting. It’s so terrifyingly clear."
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A third added: "Omg that has got to f**k the inhabitants up."
A fourth added: "The fact it's that loud underwater really shows how insanely loud it would be if you were closer."
While a fifth chimed in: "I am a diver and if you listen to this full volume with headphones it only just about recreates the real sound this person would have heard. Although recording devices sometimes have a max volume so it could be louder. Must have been quite worrying as who knows if it was coming toward you... it could get much worse."
Others said their pet animals had started 'freaking out' when they played the video out loud, while some compared it to the ocean's version of tinnitus.
There was also some debate surrounding whether Jean had actually encountered an active submarine sonar, but for the most part, people agreed that it sounded like the real deal.
Topics: Reddit, Weird, Health, Technology
Olivia Burke