He had a brief break during the thousand framer, otherwise all his animations were produced in one sweep. He took a short loop and kept adding and adding moving shapes of various kinds. For example, a curved comb shape near the bottom left keeps waving towards and away from the viewer. In the end, he creates two large pulsating shapes behind which almost all the other shapes are tantalisingly hidden. It took him around an hour of unswerving concentration to make.
Professional animators use storyboards with the sequence sketched out before their eyes.