Our analyses revealed five alpha keratins as main structural proteins of the amphibian toe pad.

FORBES: Of Tree Frog Toe Pads And Human Hair: Our Latest Evolutionary Link

Thus some parts of a frog's toe pad are in direct and dry contact with whatever they are standing on.

ECONOMIST: How tree frogs keep their grip

First, the team measured the thickness of the fluid layer between the toe pad and the Petri dish that the frog was standing on.

ECONOMIST: How tree frogs keep their grip

The extent of the delay indicated the viscosity of the fluid, and toe-pad mucus was found to be little more than one-and-a-half times as viscous as water.

ECONOMIST: How tree frogs keep their grip