Skip to 2:30, or watch the whole thing, it's not very long.
A little background info and synopsis:
This guy is not a ghost hunter, or anything like that. He just explores caves for fun and films it for his YouTube channel. This becomes clear when you take a look at his uploaded videos.
This particular video shows him going deeper into an old abandoned mine, alone, when one of the chains ahead of him starts swinging, and doesn't lose momentum.
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You know, sometimes I scare myself because I think I see things in the dark. But then I remember... If there are things in the dark looking at me, I wouldn't know because I can't see them... Then I piss myself and run.