cave
Explanation
The Joke
Two cavemen are talking. One enthusiastically tells the other, "You not been in buffalo cave? Has great drawing of water buffalo made with red ochre pigment!" The other caveman angrily responds, "Dammit, Pag! Cave ruined forever now!" Below the comic, a caption reads: "Fun fact: The very first murder was due to the lack of a spoiler alert."
The joke transplants the modern concept of "spoiler alerts" back to prehistoric times. The first caveman has innocently described a cave painting, but by revealing what the painting depicts and what medium it uses, he has "spoiled" the experience for the second caveman, who can now never see the artwork with fresh eyes. The caption takes this to its logical extreme by suggesting this social violation was so severe it led to the very first murder in human history.
The Humor
The comedy works by treating cave art -- one of the earliest forms of human creative expression -- as equivalent to a modern movie or TV show that can be "spoiled." The absurdity lies in the idea that describing a static cave painting of a water buffalo could ruin the experience, since cave paintings are not narrative works with plot twists. The escalation from a minor social faux pas (spoiling a painting) to "the very first murder" is a classic SMBC move of taking a small comedic premise and inflating it to civilizational consequences. The caveman dialect ("You not been in buffalo cave?") adds charm and sells the prehistoric setting.