From Engadget: AeroVironment recently showed off its prototype of a nano-UAV (also called NAV) dubbed Mercury. It is able to fly about and hover in place by mimicking the wing movement of a real hummingbird and, of course, be controlled completely untethered. What's more, the firm says that the final version will actually look like a real hummingbird as well, and be able to be controlled from up to a kilometer away - even inside buildings.