Thread the needle. Many know it, but few actually perform it "correctly"! Thread the needle is essentially a variation of the butterfly, a poi move in which both poi are spinning at the same time from the same position but in opposite directions. When viewed from the front, the poi appear to meet at the top and bottom, thus creating the illusion of flapping butterfly wings! The traditional butterfly has one hand slightly more on top, but the wrists are still touching and meeting in the middle. Thread the needle is just a variation of this, where you alternate which hand is on top, or "threading through". When I say that people perform this incorrectly, I mean that they don't keep their wrists together (see demonstration below). The wrists are at least a foot apart, which contradicts the whole "spinning from the same position" thing. When your wrists are this far apart, it also affects the whole "spinning at the same time" thing. I mean sure, it's okay to do it, but by definition, that's incorrect and in my opinion, it doesn't look as aesthetically pleasing!
Javier's tutorial at the top of the page gives a great & concise explanation on how to execute this move properly. If you can't seem to keep your wrists together, there is another version of this move where the hands are extended out, AKA the extended thread the needle, or extended butterfly, OR opposite direction same time extension. Click here for a tutorial on that!