Fear

Fear can can appear anytime. Prey animals live on fear and need to be constantly aware of things that may hurt them. Even sometimes things that they have seen many times before can look different that particular day.  So Tucker is a very good prey animal. In the wild he would be constantly alert to predators and things that might harm him and his friends.  
It does make it a little more exciting when your horse is constantly on alert. He has improved a lot over the last year and a half and is much more relaxed in his environment. Sometimes though things become scary when things change or are new. 
The other day a load of bags of shavings with plastic coverings that moved in the wind was dropped off outside Tuckers pen. He watched them be delivered and sit there. Then I arrived and asked him to walk by them. That was a whole new deal. It took us awhile to get relaxed enough about them to come close and touch them.  He did and was able to walk between them and around them after awhile. Good boy. So it is all about confidence. His confidence in himself exploring new things and his confidence in me, knowing that I wont ask him to do something that is going to hurt him. 

Tucker and the plastic