One of my cats sashayed up to my husband who was sitting on a hay bale in our barn and proceeded to spray mark him. I couldn't say anything to warn him for laughing so much.
His brother used to get in through open windows and crap on my son's bed.
One of the above brothers peed in an enormous box of lego. Tiny little pieces I guess he felt were a bit like cat litter. I had to wash ALL the lego. No way was I throwing away a box that big.
We had a herb garden. It needed earth. We had a load of mole hills in the back garden so I gathered them up in a wheelbarrow carefully and added them to the herb garden. Goodoh, cat litter, thought the cats, and acted accordingly amidst my poor little herb plants.
I had a pony who liked to eat the droppings of another horse - only one in particular though. He was so determined to eat shit it was really hard for the kids to pull him up and away, and then his bit would be all covered in shit when we got home.
Actually, the poo eating pony also ate the tail of that same other horse once. Just the hair of course, but he did it overnight and when I saw the horse (who was only a youngster at the time) the next day, I couldn't work out what had happened to his lovely tail - until I saw the chewed ends.
When we moved to Wales we bought a farm which had previously had cattle on it. Our springer spaniel came in from the fields that first day 'wearing' a dead calf rather as a Roman soldier would wear an animal skin.
We had a pig killed and didn't want the head. Our sons went off and buried it out in the fields. The dogs brought it back up to our doorstep. The boys buried it deeper. Back it came the next morning. My husband went out and buried it again, with concrete blocks on it. Back it came again the next morning. And you can imagine the state it was in by then.
Having had all sorts of different animals for a very long time, there are many other horrible things I could think of that they've done.