Figure 6: Actively contracting and expanding pupil armour.

This is shown in the series of ten images on the top. The drop is viewed along the E-field direction, as indicated by the crosses. At 200 Vmm⁻¹, the drop (of a radius about 1 mm) is partially covered by a clay ribbon, and at 500 Vmm⁻¹ the drop is nearly fully covered. The timescale of switching is seconds (see also Supplementary Movie 3). This is a reversible process as displayed in the bottom panel, where we plot the area of the pupil opening versus time (following changes of the electric field strength). The cartoons in the inset display a perspective view of the process.