Two of my dogs were running about in the valley behind the house. The smaller one, a miniature collie, was chasing the big one - a GSD.

The gsd ran to the top of a drainage ditch and stopped while the little one caught up. Little one comes charging up the slope to the top and the GSD just stepped back, letting the collie go straight over the edge into the ditch (it's only about a foot deep). And - this is the best part - I swear to you the gsd laughed when it happened. His lips came up and I think he was channeling Muttley.

True story.