What action—which was surprising for a man near-death—did Randy perform onstage at the beginning of his lecture?

Randy Pausch delivered the so-called last lecture in September 2007. He had already been diagnosed with the pancreatic cancer, which would take his life in July 2008. Pausch began his lecture by speaking about his cancer, telling the audience that he has undergone chemotherapy. Perhaps the most surprising thing he did, in order to demonstrate that he was in many ways still in good health, was to drop and do a set of push-ups.
Pausch wanted to emphasize that knowledge of his illness and mortality is not the only factor he considered. He made the theme of his lecture realizing one’s childhood dreams. Pausch aimed to impress the audience with the importance of having dreams and not giving up on the idea of achieving them.