Eye of newt and toe of frog.

蝾螈之目青蛙趾。

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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