TEST.  When you have a horse that is mouthy, bitey or nippy you need to ask yourself some questions. Is it all the time? Is it at a certain time? Do they do it to everyone? Your horse is trying to communicate with you – it is up to you to listen and try and understand what the behavior means. Most recently, I have had great success with the conclusion that the horse is trying to engage with me. The solution to this is to engage with their muzzle – however – you must be very present to do this because you have to be reading the situation correctly and responding in a timely manner – otherwise you will probably be bitten.