Mimic
Explanation
This comic uses the concept of biological mimicry to set up a joke about racism.
In the first panels, a mother warns her child not to go near a particular mushroom. The child asks if it's poisonous, and the mother explains that it has actually evolved a color pattern that looks like a warning but is harmless -- a form of Batesian mimicry, where a non-dangerous species imitates the appearance of a dangerous one to deter predators. The child then asks a logical follow-up: if the mushroom's warning coloring is fake, why should they still avoid it? The mother explains that the coloring mimics an actual dangerous pattern, so you'd still want to stay away from anything displaying it.
The comic then cuts to a scene with a different kind of "mimic": a man in a cowboy hat approaches and begins with the classic preamble "I'm not racist, but between you and I..." The previous panels have primed the reader to recognize this as mimicry -- the phrase "I'm not racist, but..." has evolved in social usage as a warning signal that something racist is about to follow, much like the warning coloration on a poisonous organism. The characters flee, shouting "RUN! RUN!"
The humor works on two levels: it's a clever application of the biology concept of aposematic coloring to social behavior, and it jokes that certain conversational openings function as reliable warning signals that should trigger the same avoidance response as encountering a dangerous animal in nature.