I agree with Tianimalz on that one... it not necessarily the trick. My horse, well, his nick name is "lips". Why? Because he is extremely lippy and I wouldn't dare try to teach him to kiss me. His lips are always flopping around. To teach him to kiss me would be an instant trip to the emergency room.
I taught my horse to hug me whenever I stepped by his shoulder, that trick, so far has been very safe, only problem I see is sometimes he squeezes a little to tight. But other than that its fine. When my horse gets over the random "pops" when he is irritated I will teach him to rear... he can already lay down, and has never tried doing it if I don't ask him to. I'm willing to pay the consequences if he turns into a suicidal rearer, and also, I am NOT planning to ever sell him.