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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Hold on a moment. Just going to turn on every light within 20 feet of myself.