What simile does Roald Dahl use in order to demonstrate the lithe and quick nature of Mr. Wonka's movements?

Roald Dahl uses a simile involving a squirrel in order to demonstrate to the reader Mr. Wonka's lithe and quick movements. He writes of Mr. Wonka that "He was like a squirrel in the quickness of his movements, like a quick clever old squirrel from the park" (57).