This teaches Claude how to animate things that don't stop all at once. When a character stops moving, their hair keeps swinging. When you dismiss a modal, background elements should settle after the foreground. The skill breaks down drag hierarchies (root moves first, appendages lag behind based on mass and flexibility), timing offsets (2-4 frames per level at 24fps), and settling curves that ease out with slight overshoot. Covers both UI work like pull-to-refresh elastic snapping and character animation like tail motion lagging behind body movement. The stagger formula and concrete frame counts make it actually implementable rather than just theory.
npx skills add https://github.com/dylantarre/animation-principles --skill follow-through-overlapping