The sequence is rendered flat with an alpha channel, then watercoloured in post — pigment pooling at the wash edge, granulation, a drawn line offset from the colour. In cutout mode the paper is dropped and the line carries its own alpha, so the ink reaches slightly past the wash the way it does on a real sheet.
Scroll maps linearly to frame index across the track height. The rail marks the animation's actual beats, so you can feel where the reach and the lid opening sit in the timeline.
On your site, swap the inlined frames for /assets/cubeguy/frames/000.webp … and keep the same loop.