Any Odd-Toed Ungulate with three toes should be reclassified as a Tri-Ungulate to differentiate it from other Odd-Toed Ungulate that have only one, such as a horse.
The uncontrollableback and forth circular motions made by a woman's hips when her man has made her horny but is not there to satisfy her sexual cravings and NEEDS.
My hips undulate when I'm in the saddle, riding you.
My hips undulate wildly when you are far away and we have phone sex. That's phone fucking at it's best.
When you talk naughty to me like THAT, my ass take on a life of it's own, undulating relentlessly while your words make me cum over the phone. I quiver. I convulse, I spasm. I cum. Undulating ceases.