By Richard Horgan Los Angeles (Knewz) — The first day of fall, Sept. 22, was also #WorldRhinoDay. To mark the occasion, a pair of greater one-horned rhinos at the San Antonio Zoo, one of five overall species, put the “fall” into their celebration by knocking over an installation of cardboard boxes set up by staff that spelled out “Happy World Rhino Day.” In the video, the animals feel like they are almost moving in slow motion, gently knocking over the boxes and managing to each get one briefly onto their horns. World Rhino Day is a perfect excuse for zoos across the U.S. to showcase their mem…