A few years ago, I was a frequent visitor to a public swimming pool, same day, same time. Apparently with similar swimming habits, there was an elderly person who was humming all the time. In the pool, in the shower, in the lobby, rather loud but not too much. I initially attributed it to elderly quirkiness. It was only after several encounters that I realized he was blind. The point is, I only figured that out when I saw him with a white cane outside, not at all by the way he moved inside or used the objects - he was navigating the space just like anyone else, and it was a rather crowded place. That was the day I learned that echolocation in humans is a thing.
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