Every time your cats paw hits her toy string, it swings away from her. How does this demonstrate Newton’s third law of motion?

This demonstrates Newton's Third Law because for every action there is an equal and opposite force.

Explanation:

The cat's paw hitting her toy string would be an action therefore when is swings to and from her it it creating and equal and opposite force. In other words, the cat hits it and when the string comes back to her it's coming back the same force just opposite of the direction she hit.