Okay, that's definitely cool!

Once when I was in SF, I visited the bluffy beach area south of town (forgot the name, but it's well known and a former military hangout now popular with hang-gliders -- the full size variety), and sat mesmerized for an hour or so watching artificial seagulls cavorting with the feathered ones.. No means of propulsion, no visible control surfaces -- looked just like oversized boomarangs, but they were in fact really cool RC toys..

Cheers