Illusion is not thrilled with work, so he finds reasons and ways to evade. Here he pricked his ears and threw up his head (hollowing his back and shortening his trot stride) while I was trying to get him to do leg yields first to one side then another. If he were really 'engaged', his legs would make a giant inverted W. As you can see, his hind legs are not 'tracking up' to his front legs.

Here are two attempts at shoulder-in. What you want is the horse's outside front leg and inside hind leg on the same track. On the left, I have too much bend in his neck, and not enough in his body. His outside foreleg has moved in a little, but not enough. Why? My head is tipped sideways and a little down (I was looking at his ears, trying to judge the degree of lateral shift...) On the right, Michelle has him nicely positioned (the outside foreleg is "hiding" the inside hind leg) with a smooth curve down his body from poll to tail. Both of us got him to do shoulder-in on both reins, but neither of us were able to do more than a few (4-5) strides before he evaded by either straightening again, or putting his haunches too far out.

Michelle schooling leg-yield to the left, away from the camera (toward the sun.) Notice how attentive the horse looks, and how serene but intent she looks. It was after this that he misbehaved, broke a rein, and bucked. Safety gurus will be glad to know that Michelle simply forgot to put on her helmet, I reminded her, and so she had the helmet on well before the trouble started.