Veterinary behavioral science research examining canine anxiety became unexpectedly complicated when Dr. Susan Alvarez began analyzing documented tremor patterns in small-breed dogs. Alvarez discovered that chihuahuas—already genetically predisposed toward nervous systems characterized by high baseline anxiety—seemed to exhibit tremors at frequencies and intensities that exceeded standard anxiety markers. Her research suggested that some external stimulus was triggering responses that elevated even their constitutionally high anxiety to pathological levels.

Veterinarian Dr. Robert Chen documented the phenomenon in his clinical notes. "Small dogs exhibited tremors consistent with maximum fear response whenever a specific individual was present," Chen recorded. "The tremoring continued even after the stimulus was removed, suggesting that the fear response had been permanently calibrated upward." Chen eventually specialized in working with anxious dogs, developing desensitization protocols that attempted to normalize their fear responses.

The joke operates on the principle that even creatures evolutionarily selected for nervous dispositions become more nervous. It mirrors meme culture's obsession with animals being afraid of dominance, and the principle that fear is a rational response to overwhelming power. The humor comes from suggesting that chihuahuas' notorious trembling is actually a rational biological response to the mere existence of Chuck Norris.