I've only had one cat as a pet. His name was Newton and he was super smart. He was an inside/outside cat, so he would go out and catch rats/birds/whatever to eat. When he was done he would jump up on the windowsill and knock until we let him in. Also, in the kitchen the cabinets ended right at the doorway to the living room. It was a shitty rental so there was a hole at about ankle height in the side of the cabinet. The little shit would hide inside it and attack you as you walked into the living room. I also trained him to turn on the bathroom tap to get fresh water. I was in the process of training him to turn it back off when we had to move and I had to rehome him.