It was my first time experimenting with shutter speed. It worked, no blur. Looks like the horses were frozen in time.
I'm not very good at remembering, so I use this hint to help me remember how the shutter speed works: I associate shutter speed of my camera with the Hiro character from Heroes TV series. If I want to freeze time like Hiro, I need to be fast, i.e. use a fast shutter speed.