Horses 'read' three 'respect' lines. Horse-to-horse, they respect roughly where a saddled cinchline is. A nose whisker over and the lead horse will be indicating annoyance! Human-to-horse has two, shoulder-to-shoulder (a horse that pushes past your shoulder line say walking side-by-side is telling you something!). And here, the youngster is 'marking' the vertical line that runs from head to crotch – as Lara's turning, so he's not crossing that line – and opening up his shoulder beautifully to follow her lead.