Great shot. I can understand the caution. I'd be afraid the horse wouldn't realize where the hay stopped and the hand begun. Especially since I watched my Grandpa get and chuck bit out of his arm while carrying an armful of hay.
This reminds me of visiting my grandparents' farm when I was about that age. I had an unpleasant encounter figuring out that the fence had electricity running through it.
A great candid shot.