I hear comments about horses not being very smart all the time. But I think they just might be wickedly smart. They may even have a keen sense of humor. You just have to pay attention.
Take Dino, for instance. Now I admit that Dino hadn’t been as “active” as a 3 year old horse should be. It had been incredibly hot, so he had mostly just been getting turned out. That’s when “this” started. 3 times in one week, my giant dinosaur of a horse used his automatic waterer for a toilet. This is no accident either. Dino’s normal “relief station” is at the very other end of his paddock. This is an intentional message. A plea for attention. When the weather cooled, and Dino was back to his normal exercise routine, this nighttime activity ceased. Yep, Dino, I got the message loud and clear (although I really fail to see the humor in this). I just wish you would communicate in a way that was a bit easier to clean up!
Del Mar Horse Girl 
That’s pretty funny! Our mare used to do this on occasion, but it was usually when she was scratching her butt on the water bucket!
Ok I can sort of understand an itchy butt, but getting it into the little waterer 3x takes some serious skill. This waterer is too low for itching and it is wedged between a bucket and a large water tub. He really has to back in and aim! Goofball horse.