Part 4: As the riders progress to the water element, Christopher gives a demonstration on using the rein aids, including how to make a single bridge and how to change the whip on course. He explains how easily a single bridge allows the rider to slip or shorten the reins, and suggests everyone practices whilst hacking to get comfortable with having the reins in one hand. One rider learns to ride more aggressively to help her horse who tends to slow coming into the water, while another practices giving up control to allow the horse to have more rein on the approach to the water. All the riders struggle to give a long enough rein, and Christopher works with them to allow the horses their neck through a jump.