Shape. The body, cephalofoil, fins and tail lobes are one signed distance field —
capsule chains and rounded boxes blended with smooth-min, with the mouth and the notch in
the hammer cut by smooth subtraction. The surface is extracted once with surface nets and
re-skinned every frame.
Soft body. Inside sits a 22×5×7 XPBD lattice: hexahedral cells with shape
matching (Horn quaternion fit) and six tetrahedral volume constraints each, plus distance
constraints on edges, face diagonals and cell diagonals. Stuffing sets how hard the
particles chase their animated rest shape.
Swim. A travelling S-wave bends the cells' rest shapes side to side, ramping up
toward the tail; steering bends the rest shapes into an arc so the body curves through
each turn. The lattice lags behind, and that lag is the jiggle.
Fur. Alpha-to-coverage shells over the minky pile. Each shell is offset along
the skinned normal and along a per-cell comb field you can groom with the Comb tool;
strands are hashed in 3D on the bind pose so they stay put while the plush moves.
Mouth. A hinged lower jaw swings on a lateral axis; felt lining, embroidered
gill lines, a stitched belly seam and glass eyes on the tips of the hammer are shaded
procedurally in the fragment stage.