The clip is held in the rifle by a finger in a hole on the side. As the lifter moves up to the top, that finger is withdrawn, and YIPPEE! Ping! There is enough force in the operating rod spring to send it out. It is a complicated mechanism.
There is a way to cross two rounds in an as-issued clip and lay the three parts together in the receiver. They align themselves again, and the shooter can do the USGI thumb-the-nose salute to John Garand. If you are going to do sell tickets and the Ping! is the thrill, the range assistant will be able to perfect their drill pretty quickly.
Youtube - "How to load the M1 rifle with 2 rounds"