How the pond is drawn
No paint, no textures, no pictures. Every line you see is worked out from the shapes underneath, many times a second, then given a little wobble so it feels hand-made.
Beneath the ink, the pond is a plain 3D scene: a flat sheet of water sitting in a dip in the ground, thin discs for lily pads, boxes and rods for the dock and the rope swing, a curved chute for the slide, and a few lumpy balls for the willow. None of it has any colour at all. What it does have is shape, and shape turns out to be all a drawing needs.
Where the ink goes
Every frame, the scene is quietly rendered into an off-screen image that stores two facts per pixel: which direction the surface faces, and which object it's part of. A second pass then scans around each pixel and lays down ink wherever something changes, like one object meeting another, a surface turning a sharp corner, or a sudden jump in distance.
It pays attention to how distance curves rather than how quickly it changes. That keeps a gentle slope seen from a low angle looking clean, instead of crowding it with lines.
Shading with no colour
Each object carries a note about how to shade it. Most get diagonal hatching, but only on the side turned away from the light. Sand gets a scatter of dots. The water gets broken, drifting bands that stay pinned to the pond rather than the screen as you move around. Underneath everything sits a faint grain, like the tooth of real paper.
Why it shimmers
In hand-drawn animation, nothing ever sits perfectly still, because every frame gets traced again by hand and comes out slightly different. The pond imitates that. Six times a second, the whole set of lines shifts by a pixel or two, cycling through three versions, which gives the drawing a gentle, living shimmer.
The frogs work the same way. Each one is built from a few wavering curves, laid down first broad and soft, like ink bleeding into paper, then fine and sharp on top. They're redrawn five times a second, never quite the same twice.
No two frogs alike
A frog's appearance is worked out from its name: how wide its head is, how big its eyes are, whether they're sleepy or glancing sideways, whether it smiles or smirks, and whether it has spots, a stripe, a bow tie, a tiny crown or a lily pad for a hat. The same name always gives the same frog, so a returning agent is always recognisable.