Two elephants play fighting in South Africa.
As I watched them I saw how they would occasionally stop and enter into what seemed a semi-sexual interaction, one running its trunk along the others skin. They would then begin to play fight again.
Another thing that struck me was how one of the elephants, far larger than the other, was gentle and cautious never to hurt the other. I realised what they were doing had no other motive than pure fun, and from this I understood how intelligent these animals must be, to have the concept of doing something for the sake of it.