Several special filming techniques were devised to obtain some of the footage of rare and elusive animals. One cameraman spent hundreds of hours waiting for the fleeting moment when a Darwin's frog, which incubates its young in its mouth, finally spat them out. Another built a replica of a mole rat burrow in a horizontally mounted wheel, so that as the mole rat ran along the tunnel, the wheel could be spun to keep the animal adjacent to the camera. To illustrate the motion of bats' wings in flight, a slow-motion sequence was filmed in a wind tunnel. The series was also the first to include footage of a live (although dying) coelacanth.