The word "哎呀" is formed through the reduplication of two phonetically similar characters, both containing the mouth radical (口), which semantically signals a sound or exclamation. The repetition of the open vowel sound "ai" in each syllable ("ai" and "ya") creates an elongated, spontaneous vocal expression that mimics a natural human utterance of surprise or dismay. This structural formation turns two independent, sound-imitating characters into a single, reinforced interjection where the whole is greater than the sum of its parts, capturing a complex emotional reaction in a single breath.