Caustics for a toy model of an individual and isolated ψDM perturbation. For this example, the ψDM fluctuation is positive. The left and right panels show the caustics produced by the same 2 pc-scale ψDM fluctuation, but on the two sides of the lens CC and at the same distance. That is, they represent the fluctuation in the positive- and negative-parity sides with the same macromodel magnification. In both cases, the macromodel magnification is 160. The caustics are almost indistinguishable, with just a small shift in position. The white dot marks the same position in the source plane, so the shift of the caustics with respect to this point indicates the shift in position when we vary the parity. A negative fluctuation in the deflection field of ψDM (not shown) results in similar caustics, but which are mirrored in the horizontal direction.