Odd Plane

So I looked up to see what appeared to be an airliner. It looked odd. It was either very big or flying lower than usual. Indeed, the other planes flying this morning were leaving contrails, but this one didn't. So I pulled up flightaware.com and found this. That seemed pretty odd, too. So I did a search for the identifier, BOE521, and found this as well. Turns out I was watching one of the new Boeing Dreamlifters on some sort of test flight. Cool.