The word "咕噜" (gūlū) is a classic example of a Chinese **reduplicative onomatopoeia**, formed by repeating a single-syllable phonetic unit to mimic a continuous or repetitive sound. Its formation relies entirely on phonetic imitation, where the syllables "咕" (gū) and "噜" (lū) together simulate the sound of something rolling, gurgling, or rumbling, such as stones tumbling, water bubbling, or a stomach growling. The character choice is phonetically driven, often utilizing the "口" (mouth) radical to visually signal its sound-imitating function, and the reduplication creates a rhythmic, descriptive effect that emphasizes the ongoing or rolling nature of the noise it represents.