We have a foal at my aunties that if you scratch her tummy, her back leg twitches, she streched her head and her lip sticks out haha.
Sadly, she might be put to sleep because of a wire cut :( But we will see if she improves.
My guy loves his cheeks scritched. Some horses like right behind their elbows scratched; mine does after a workout. He also likes his chest scratched. He's also learning to enjoy a good poll rub, especially when I'm riding, and he gets some bugs up there!