Before scientists could understand flapping flight, they first had to see it in the minutest of detail. In the 1970s, Torkel Weis-Fogh, a Danish zoologist at the University of Cambridge, used high-speed photography to analyze the exact wing motions of hovering insects and compare them to the insects’ morphological features. From this, he formulated a general theory of insect flight, which included what he called the “clap-and-fling effect.” When insect wings clap together and then peel apart between the up and down strokes, the motion flings air away and creates a low-pressure pocket. Air then rushes back into the pocket, forming a swirling vortex. This vortex creates the force necessary to lift the insect between wing flaps. Similar vortices might be generated by the angle and rotation of the wings, Weis-Fogh posited, providing additional lift.