Inextensible membrane. The wing is a grid of points whose distances from each other cannot change — like real cloth. Flap torque propagates through the constraint solver, so waves travel and reflect the way they do in a live manta's pectoral fin.
Passive tail filament. The tail is not animated — it is simulated. Each segment follows the one ahead of it with stiffness and drag, producing that natural trailing whip for free.
Rendering. ~58,000 points per frame plotted directly into an ImageData buffer: Lambert shading, rim light, specular highlights, and an algorithmically placed ocelli (spot) field. No textures, no 3D engine — just math.