The word "哼哼唧唧" is formed through the reduplication of two onomatopoeic characters: "哼" (hēng), which mimics a grunt or moan, and "唧" (jī), which mimics a chirp or squeak. By repeating each character in an AABB pattern, the combination creates a compound expression that phonetically imitates continuous, indistinct sounds like muttering or whining, emphasizing the repetitive and prolonged nature of the action it describes.