I am curious to read personal anecdotes any of you may have about physical phenomena that are not seen very often. I don't mean deliberate observations in a laboratory setting. Just something that happened when you were not expecting it. For instance, supposedly the sun as it is setting (or rising?) can sometimes seem to give off a green (?) flash. I have no idea what that is about, or if it is true. I have never seen it happen. Also, pilots speak of something called a "glory" which is kind of a halo that is sometimes seen near clouds. Ball lightning sounds wild and crazy, but it has been observed enough times that it is likely to be for real. As for me, I can think of two things that happen rarely enough that I have only experienced them once each. One morning I was stopped behind a cement truck at a red light. It was cold (by desert standards, anyway) and there was no discernable wind, if those are parameters that matter. When the light turned green and the truck driver hit his throttle, a smoke ring came out of the vertical exhaust pipe's open end and rose slowly up into the air. I watched it rise for a good 5 seconds. Other than that, I've only seen smoke rings coming from the mouths of smokers. One day I wanted to cool a cup of tapwater quickly, so I put it in the freezer. When I took the cup out of the freezer, I noticed it was completely liquid; there was no skin of ice on it. I put it up to my lip to drink it, and the moment the water touched my upper lip I felt a funny sensation and heard a sound coming from the cup. I pulled it away from my mouth, and the cup was full of opaque white slush. I take it this was an example of supercooling, and my lip provided a surface for freezing to start, and the freezing propagated from that point to the rest of the water in the cup over the course of about one second. It probably says something good about whoever had washed the cup.