Some kind of weird, complex variant of a comic strip randomizer, based on something called a Markov Chain. I don't get the math behind it, but the results are hilarious!
I can't post a strip because the dialogue gets overlaid onto the strip image by a generator, so here's a link to the site instead:
Garkov -- Garfield + Markov chains -- Josh Millard
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EDIT:
Found on another weird Garfield mashup website:
and