A classic trick by none other than Doctor Popular (aka Doc Pop) himself. You show me a yoyoer who doesn't know Skin the Gerbil and I'll show you a yoyoer who's been living under a rock.
The yoyo has to spin for quite a while to do this trick, so make sure to keep the string centered in the gap of the yoyo as you're swinging it around.
Oh, and another thing. Lately people have been renaming this trick "Gerbil." PETA probably called someone about animal abuse and threw everyone into a tizzy, so now the name has been politically corrected, but I'd rather do Doc Pop justice and keep with the original name, even if it is a little cruel.