I've started working with one of the horses at the barn and I've noticed that when I ask him to do a game such as "Hide the Hiney", he pins his ears back but shows absolutely no aggression towards me. With all the other ground work we do this is the only game in which he does this. He is a very gentle horse and always does what I ask. I was just wondering why he is pinning his ears back and is it something I need to be concerned about? Also if it is a concern how can I teach him to not pin his ears back when playing games? Thanks for all your help!