Some of them are difficult to answer in 140 characters, so there's a bit more explanation in the video. I learned something I didn't know about double rainbows when Bill replied, "In a sense, there's always a double rainbow, but the 2nd one is much fainter. The sky has to be dark enough for you to see it."
Also interesting is that many of the Twitter users whose questions were answered have not responded. Someone should tweet the video to Insane Clown Posse, because one of the answers is about f-ing magnets and how do they work?