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When the horse's hind leg impacts the ground, that will be the right time for the half halt."
"Before you ask your horse to make a different move, as from walk to trot, you must prepare him with a half halt, asking him to be attentive and rebalance his body so that he can dance into the next movement easily and with brilliance. You must also use the half halt to rebalance the horse as needed, throughout the movement. Be sure your hands lighten at the end of the half halt to reward your horse and allow him to go forward."
"You can make the half halt more powerful by simply adding to your centering any of the following: stronger legs into hands; legs into stronger hands; or inside leg into outside hand at a corner. You can whisper a half halt by simply centering yourself, but whether it is a whisper or a shout, it should never be a jam-the-rear-into-the front process. It's more of a dance instead."
"You always half-halt by driving onto fixed hands — never by simply taking on the reins."