So, it looks like the XKCD comic has, perhaps inadvertently, declared me a "flake," for you can also count me as someone who has observed optical and/or atmospheric phenomena which I cannot explain, including tiny dots of light in the night sky making sharp 90-degree turns, and no less than eight text-book cases of flying triangles across a span of a few days. While I reserve my judgement that these visual anomolies are extraterrestrial in origin, I confess that I also believe (note my choice of words here) in extraterrestrial visitation based on historical artifacts and other evidences. Correlation is not causation, hence my reservation of judgement. Nonetheless, until Randall Munroe can offer more concrete explanations, I would strongly urge him to refrain from delving into the public humiliation cesspool that is ufology. I read XKCD for the elevated humor, not for elementary-school bullying.