This summer I spent an hour watching a pair of magpies harass a fox. The fox was trying to sunbathe, but the magpies kept dive-bombing it, pecking its tail, and landing in front of it then flying away just as the fox went for them, all while making a chattering sound that seemed a lot like laughter. I've heard theories that they do this as revenge for stolen eggs, or to chase foxes away from their nests, but this was in an open patch of ground far from where they nest and it really looked to me that they were just teasing it for fun.