I find many folks interpret the act of riding one horse and ponying the other as a way to get the unridden animal to follow the other one. This can create mindless movement in the ponied horse and contribute to what seems to him willingly complying, but is not thoughtful, mentally available interaction.
I use ponying as an opportunity to continue the Conversation I'd started with the horse while initially working from the ground. This includes directing the ponied horse's thought, specificity of his movement and his energy.
There should be no drag on the lead rope, the ponied horse should not be staring at my riding horse avoiding the world around him, and he should not feel challenged by working alongside another horse.
The tool of ponying a horse can expand his understanding and acceptance of spatial and physical pressure, can offer him the chance to learn to interact with the human despite another horse nearby, and allow him to search for how to address the human's input.
Too many folks don't prepare either the riding or the ponyied horse and things can quickly escalate into unnecessary stressful and potentially dangerous situations when concepts like softening to pressure, letting go of a thought, pausing to check in with the human haven't been established beforehand.
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