I saw a pretty amazing thing during my flight from Dubai to London, seeing another plane fly past! During sunset!
You may not find it intriguing as me, but the reason I was so amazed was not too long ago from 9gag there was a post about getting perspective of how fast planes actually fly. You know when you’re sitting in your seat it seems to be barely moving. A video of another plane flying in the opposite direction close-by really shows how fast you move.
That evening on the flight to London, I witnessed that for myself, but to top it off, it was sunset and the plane was leaving behind a condensation trail.