It's October -- the month for spooky things barely glimpsed out of the corner of your eye. Hidden things. Secret things. But there's no need to go all supernatural about it: plenty of natural events happen beyond the limits of our senses, making them as mysterious as any hypothetical ghost.This month, at least twice a week, we'll look at phenomena that are normally too fast for us mere humans to see. First up, a film from one of the pioneers of ultra-fast photography: Harold Edgerton: Popping a Soap Bubble.