Well, this isn't exactly an 'inexplicable' phenomenon, but a few years ago I was at home alone, footering about. Suddenly, I heard a rumbling, and the window frames strted to rattle (old building, single glazing) I ran to the window, and the noise got louder - I thought maybe a plane was flying really low, or about to crash. My dog started howling, and outside, car alarms were going off. Suddenly, shooting across the sky, a large, crackling ball appeared. I had not a clue what it was, but I was scared. I thought the world was about to end - I phoned my partner because I was convinced an apocalypse was imminent (well, that's how the dinosaurs died - I thought I'd seen a meteor or something) Turns out it was ball lighning, a very rare phenomenon.