My family's horses are full of quirks! My grandfather's Colorado Ranger mare loves to have her neck and the underside of her jaw scratched. She will turn her head nearly upside down, wiggle her upper lip in the air and nearly fall over when you scratch her. She loves it! She doesn't scratch herself on fixtures or seem itchy in any other way either. She just likes it when a person uses their nails. I will have to get a video of this someday.
This horse is also an escape artist. We have stalls with removable yolks so we can choose whether to allow the horses to put their heads out of the stalls or not. Foxy cannot have her yolk out. It only takes her about 5 minutes to jimmy her latch open. She manages to get out in the middle of the night once. We're not really sure how because her yolk was closed. The sliding barn doors were closed so she couldn't get out of the barn but she made quite a mess of the barn. She ate the bristles off one of the brooms, rearranged the stuff in the wash stall, and went at least part way up the stairs to the hay loft because the hay was cleaned up off the stairs. I have no idea what we would have done if she made it all the way up the stairs and ended up in the hay loft!
My grandfather's one OTTB is known to steal hats off people's heads and run away with them.
His other OTTB is notorious for playing in water troughs. We keep three water sources in her pasture in the summer, in the hopes that one of them will still have water in it by the end of the day.
My dad's appaloosa mare will sometimes try to mimic sounds. I just recall this one hilarious incident when I was waiting outside the arena at a show with her. I had my gloves in my hand and was slapping them back and forth in my hand. Queen then stuck her tongue out, slapped it back and forth on her cheeks and made the same noise. She did it more than once and looked so silly doing it. My mom and I were dying with laughter.
I'm pretty sure my horse's lower lip is too big for her. It's never tucked up against her teeth like normal horses. It's always hanging loose, like some horses do when they're relaxed but my horse is like that pretty much all the time. Her previous owner called it her "sugar cube drop box" When her lip is hanging particularly low I can fit my whole fist inside the space. The funny thing is, she'll let me do it. My husband has a habit of walking up to her and just grabbing her lips and playing with them, and she's completely okay with it.
Here's a typical expression on my horse's face. Note the gap between her lips. From the outside she almost looks like a monkey mouth but her teeth line up just fine. Lol.