Figure 4.

Adhesive force and work of adhesion of the frog tongue, measured in a quasi-static test. (a) Time sequence of an indenter pulling away from the frog tongue. The tongue deforms greatly before separating. (b) Schematic of the quasi-static test. (c) Relationship between force and displacement. Experiments denoted by points and mathematical model by solid lines. Various retraction speeds are shown including (black), (red), (orange), (green) and (blue). Inset shows model predictions of the average contact radius. (d) Work of adhesion for each retraction rate. Experiments are solid colours, with theory overlaid in hatched colour. (e) Tongue peeling as the indenter is displaced. The tongue is visualized through a transparent acrylic indenter. Graph shows that the average contact radius decreases linearly with displacement.