My cat Nussy understood 'no' 'come' and 'stay'. He would tell me when it was dinner time and if I said 'stop nagging, I know' he would think I'd said 'no' and I'd have to get up quickly and get his meal or he'd go out hunting.
I also trained him to think he was being given tablets as a reward for being a very good cat (using hoeopathic blanks from kittenhood) so dosing him was incredibly easy.
He went out one night about six years ago and never came back - probably hit by a car.