From a short history:
[Joseph B.] Friedman inserted a screw into the straw toward the top. Then he wrapped dental floss around the paper, tracing grooves made by the inserted screw. Finally, he removed the screw, leaving a accordion-like ridge in the middle of the once-straight straw. Voila! he had created a straw that could bend around its grooves to reach a child's face over the edge of a glass.