Tennis racquets at the local sporting goods store are typically strung with synthetic materials such as nylon. The pros, however, prefer the natural stuff—and it’s not catgut as commonly believed, but cow gut. Less stiff than nylon, natural strings offer more control. It’s also more expensive: one cow can only string three racquets.

With their composite frames, today’s racquets are an engineering marvel that enables pro players such as Rafael Nadal to topspin a tennis ball at 3,600 revolutions per minute, as Ainissa Ramirez, a Yale University professor of mechanical engineering and materials science, describes in her Science Xplained video here. She originally made the video in July to coincide with Wimbledon and the New Haven Open.