It's done fast. At first it feels impossible for your middle and ring fingers to move at the speed necessary to do the change.
Keep practicing and you will gradually get better at it.
that might happen at first, but just keep practicing, its suppose to kinda go around the pinky. when i first learned it, i was like : WTF? THATS IMPOSSIBLE *doesnt practice, makes own variation =)* but then i gradually started practicing more and more...then it became more natural. so i guess the best tip is to just practice, even if it seems impossible, keep practicing til its perfected =)