Animal behaviour can often surprise us, but we have to be careful how we interpret it.

Those rats certainly seem to be displaying pleasure, or perhaps it is that sort of hysterical response some people also have to tickling. This is not the same as self generated laughter, when laughter is spontaneous, and not necessarily initiated by something/one else.

I 'd love to think animals can laugh. There is a marvellous moment in one of David Attenbourgh's documentaries on elephants, when one of the huge adult elephants realises there is something suss about the camera (it's hidden in a pile of plastic elephant poo). She plays around for a while----and after thinking a bit she stamps on it and throws it away with what almost seems to be a cheeky grin. It's quite deliberate and very funny. This doco also has the roaming elephants discovering the bones of one of their companions. They stop for a long time, handle the bones with their trunks and sway backwards and forwards. It is tempting to believe they recognise her, and mourn her, but that may be a step too far.

By the way, if you have had a cat live with you (you never own them) you will know that some of them hate being laughed at. The one we have at the moment will stalk off and sit on the other side of the room, with his back to us when we do. So of course we laugh even more!