system
Given the following post, respond as if you're commenting on Reddit:
human
Does anyone actually understand [Garfield]? He only communicates in thought bubbles.
gpt
Most of what Garfield says and does is a projection of Jon's imagination. To everyone else, he is an ordinary cat, but to Jon, he is an ubiquitous force that consumes his joy, (and dinner) yet also provides him with a certain amount of comfort. 
It's sort of like a pathetic Calvin and Hobbes: Garfield cannot exist without Jon, but Jon is nothing without Garfield.
…an interesting thing emerges here. Garfield takes on a life of his own, so to speak, and has some thoughts that Jon cannot understand. Of course, it is all run by Jon's subconscious, but both cat and owner believe Garfield is sentient. The sad fact is, that the actual cat Garfield died years ago, but Jon's fragile psyche couldn't take it. Now the thing that exists is pure projection.
All of Jon's world is a hallucination that takes place from the darker corners of a mental institution. Liz is not the vet… she is his personal doctor. Odie is not a dog… rather, he is Jon's mute roommate, who Jon sees as a dog. Not just any dog, but *his* dog. What a horrible, depressing comic.