I have flown my mavic pro at an outdoor horse show with the prior permission of the landowner and organiser. I have the quieter props fitted, but it still sounds like angry bees. I kept at least 50 feet altitude, tried not to be directly over any of the horses and all but one of the 100 or so horses and ponies showed little or no interest in the drone. One horse got very agitated and spooky and the rider had to dismount blaming the noise of my drone as the cause. When I became aware of this I landed immediately and shut down my drone. I then went and apologised to the rider and assured her I would stay grounded until she left the show. She was as agitated as her horse and was quite abusive to me, so I apologised again and walked away before the situation deteriorated any more. I then went and informed the show organiser what had happened and was advised that the horse spooking was more the riders fault than my drone as it had been showing signs of agitation even before I took off.