Shoulder Pop is your introduction to counterweight redirection using your body.
Before we were just waiting for the counterweight to simply redirect itself. The main idea of Shoulder Pop is that you can throw the counterweight with the purpose of using your body to send it the other way to mount the yoyo.
Start with any under mount and let the whole string formation rest on the throw hand. Now, summersault the whole formation forward, allowing the counterweight to dismount and travel around. Stick your arm out and let the counterweight hit your shoulder.
This should kill the momentum of the counterweight and lazily send it back for you to re-mount the yoyo in an under mount.
This will prove to be very useful in later levels of 5a play.