Clearly, the Coen brothers were in dire need of an animal trainer who knew what they were doing. The old notion of cats being "aloof" and "untrainable" is about as antiquated as the view that dogs "need to be shown who's boss" or else they take over the pack.
Cats (along with most other animals including us) respond extremely well to positive reinforcement focused training methods. They get their "untrainable" tag because contrary to dogs, you can't "make" a cat do anything. But you can motivate them do almost anything with the right training approach. And, along with a well trained cat, you get a pretty sociable one too.
Whilst training dogs with positive reinforcement is gaining traction around the world, the way most people view cats has not followed suit, as the Coen's example shows. Fortunately, things are changing, with trainers and behaviourists such as Pam Johnson-Bennett and Karen Pryor publishing books and online information about training (and better understanding) cats.