In "The Last Dog," the phrase about Brock becoming "crippled by his primal urges" refers to his struggle with instinctual behaviors and desires that emerge in the absence of civilization and societal norms. Brock, a dog who has survived in a post-apocalyptic world where humans have disappeared, has reverted to more instinctive animal behaviors as he navigates this harsh environment.
This transformation highlights the theme of survival and the conflict between his learned, domesticated behaviors and his inherent instincts. The "primal urges" may include instincts related to hunting, territoriality, and reproduction, which can complicate his decision-making and make it difficult for him to connect with both the world around him and his internal sense of self. Ultimately, this struggle underscores the tension between his animalistic nature and the remnants of his domesticated upbringing.