Your first reaction is to stop him and explain that you want to be the boy, not the horse, but then you realize this could be really interesting. The barber said he made house calls - apparently, he will change you back in a month. And the horse looks really powerful in the photo.
By this time, it's too late anyway. Your face flows out suddenly into a muzzle as he finishes forming the shaggy, tangled mane that is your new 'haircut,' the barershop fades away, and you are standing on four legs outside of a weathered barn. You are aware of a slight pressure on your back - the teenager you were orignally planning to become. As big as he is, you can barely feel his weight.
You feel wonderful. Colors are off, and sounds and smells are much stronger. Being a horse should be really strange and confusing to you. But as the boy dismounts, you find yourself perfectly comfortable as an animal.
The boy is your master - you recognize his smell, and know you have been his for several years, ever since you were a foal. The barn is where you live. Something else seems strange, though. You can't quite place what the difference is.
The boy moves around and opens the barn door. "That's enough for today. Go on in to your stall, girl. I'll bring you some oats."
Girl?! A quick shake of your hindquarters confirms that you don't have anything swinging between your hind legs. The back part of the horse wasn't shown in the picture - now you know the boy was riding a mare!