This is a good exercise to help supple your horse and encourage equal bending on each rein. It consists of 3 or more (depending on the size of the school) half circles joined together with straight lines, giving you plenty of time to change bend from one side to the other as you cross the centre of the school. It is also an opportunity for you the rider to think clearly about your bending aids as they need to change for each new loop (i.e. your outside aids become your inside aids and vice versa for each new loop). Take care to maintain energy and rhythm and prevent any falling in or out on the half circles. Change your diagonal each time you cross the centre line. If you want to make this exercise a bit more challenging (and interesting), you can add a 10m circle onto each loop - making the serpentine into a series of 10m circles joined with straight lines.