Instructions
Make sure that your yo-yo has a concave shell, otherwise you will not be able to do the trick. Most yo-yos have a convex shape with a rounded casing. You need one that curves inward so that you can stick your thumb underneath the yo-yo's edge.
Release the yo-yo straight to the ground. It should be suspended and spinning with great force. Some people prefer to form a trapeze at this point in order to speed up the yo-yo's spin, but this is not absolutely necessary.
Yank the string upwards with a jerky motion, causing the yo-yo to rise up to eye level. The yo-yo should still spin while it is in the air.
Follow the yo-yo with your eyes. Wait for it to reach its highest point and then fall a few inches.
Slip your thumb underneath the shell once the yo-yo has fallen two or three inches. You want your hand's motion to accompany the fall of the yo-yo. When your thumb makes contact with the yo-yo, it should be moving slightly downwards to pick up some of the momentum of the yo-yo's fall.
Allow the yo-yo to rest on the thumb for a few seconds. This is the climax of the trick.
Push slightly upwards with your thumb, forcing the yo-yo to rise off of the top of your thumb. Pulling your thumb out without a slight upward motion may cause the yo-yo to spin out of control. You want to carefully control the yo-yo's motion.
Wait for the yo-yo to drop all the way to the ground and spin for a second. At this point, pull it back up into your hand.