My sister had a cat , when I was a kid , a beautiful solid black cat she named Sacca . When she got married and moved to Germany husband was in the Military , we kept the cat . I woke up one night , in what used to be her bedroom it was the 2 nd biggest bedroom and I moved into it when she got married , with the doorknob rattling . This goes on for a couple minutes , then suddenly the door cracks open . In pops the cats head . It had learned and we caught him doing this later to turn a normal circular door knob . It would jump and hold the handle and just shake until it turned it enough . Was freaky . This same cat , without training , occasionally used the toilet . I walked in one day and it was just sitting on the toilet , using it properly . He only ever peed in it , but it was the strangest thing . Have attempted to train two cats since then and neither would have anything to do with the toilet .