Horrifying Laughing

One of the most haunting sounds that I have ever captured. I got on the bus one day and didn't notice anyone on there when I sat down, and then a few moments later, I started hearing this sound. I was confused as to what to do. Do I turn around and look at this laugh-er in the face? What would a person laughing like this do to me if I looked at them? How could a person even laugh like this? It doesn't sound physically possible. As more and more people got on the bus, I saw nobody looking in his direction either. Am I maybe imagining this sound? IS THERE A TINY MANY LAUGHING IN MY HEAD?

Upon leaving the bus, I looked back and couldn't tell who must have made the sound, but regardless, it still literally shakes me a bit hearing this audio.

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Recorded with an Android phone and edited in Audacity