Birk called me yesterday, out of the blue, while I was at work. He was nearly speechless. See, his sister had called him and asked him to go look for something in her room. He did, and didn't know that Gimli (our cat) had followed him. Before he left the room, he heard something in the bathroom that sounded like a leak, so he investigated. It was Gimli, using the toilet for its intended purpose.
I would like to emphasize that we have never made any attempt whatsoever to teach Gimli or any of the other animals in the house to use the toilet. (I have seen the other two cats and the dog drink out of them, though.)
I knew Gimli was smarter than he let on. All that batting around leaves and balls of foil is just an act.