The word "大喊大叫" is formed by combining two nearly synonymous and parallel verb phrases, "大喊" (to shout loudly) and "大叫" (to yell loudly). This is not a grammatical structure but a conceptual one, using repetition and reinforcement to create a single, amplified idea. The two parts mirror each other in rhythm and meaning, merging to vividly depict a scene of continuous, chaotic, and emphatic loud vocalization, thereby intensifying the sense of noise and unrestrained emotion beyond what either phrase could convey alone.