Natural Training?

Although, when kept in reasonable conditions, horses are generally very peaceable, they will bite or kick each other hard enough to draw blood and cause significant injury. They will (rarely) show true aggression towards each other, for example trying to break each other's forelegs. 

So, if someone tells you it's OK to do something, such as chase your horse round a small pen, because it's 'natural' behaviour and they understand it, don't ever accept this as a reason for doing it! Some of their natural behaviours are designed to expel, injure or even kill each other so we should be very careful about which we choose to mimic.