Today my horse took off with someone?

[joann]

Since your horse took off after FB leaned forward after an encounter with a branch she may have interpreted that as a signal to do what she wanted to do anyway, which was to keep up with her horsey companions. It is also possible FB was radiating fear at that point and your horse lost confidence in his leadership taking things into her own hooves. It is also possible that FB isn't the world's most secure rider and without knowing it cued your horse forward by tensing his legs. It is also possible that your horse was annoyed with FB if he lounged in the saddle or was otherwise sloppy in how he cued her, and that she took the slightest excuse to be exuberant when the other horses were cantering.