I was at the bottom of a round, improbably deep pool (well?). When I looked up from the depths, I saw a zebra racing around the top edge. With each lap, it would reach a point at which it would stop so abruptly that it would nearly lose its balance. I was terrified that it would fall and be injured or killed. I also wondered if my looking at it was startling it and causing it to nearly upset itself at the same point in the circumference.

Then the pool was suddenly normal in depth, and the zebra was gone.