many-moons
Explanation
The Joke
The comic depicts what appears to be a time-travel scenario. A modern-day scientist, Dr. North, has traveled back in time and encounters a caveman. The caveman speaks in a stereotypical "caveman" dialect: "Me am from many moons from now! You--" But then the caveman immediately breaks character and corrects himself with surprising linguistic sophistication: "Am caveman. Find use of articles and pronouns confusing only. Am otherwise fluent." The caption reads: "Moments into the first time traveling expedition, Dr. North commits a faux pas."
The joke subverts our expectations about how cavemen would speak. Rather than the time traveler being the one to struggle with communication, it is actually the modern person who commits a social blunder -- presumably by assuming the caveman would speak in broken, primitive language. The caveman, it turns out, is perfectly articulate and self-aware about the specific grammatical features his language lacks.
The Humor
The humor comes from the reversal of the expected dynamic in a time-travel encounter. In most fiction, the time traveler is the sophisticated one who must simplify their language for primitive people. Here, the caveman is the one who is linguistically self-aware, calmly explaining that his dialect only differs in its handling of articles and pronouns -- a remarkably precise piece of grammatical self-analysis. The term "faux pas" in the caption is itself a sophisticated French expression, adding another layer of irony. The comic pokes fun at the condescending assumptions modern people might bring to encounters with people from other times or cultures, while also being a playful riff on historical linguistics.