Figure 2.15 — Trapping non-convex shapes and windmill effect Figure 2.15 — Trapping non-convex shapes and windmill effect. (a) Multiple scattering of a ray on a complex shape constituted by two spheres one inside the other; this is a simple optical model for a cell containing a nucleus. (b) The asymmetric deflection of the incoming rays on a non-cylindrically-symmetric object produces the torque indicated by the black arrows and the rotation of the object. This phenomenon is known as the windmill effect.