Pure nasal exhalation with no vowel - written as bare 'hng' because the sound has no syllabic core. Used only as a standalone exclamation of dissatisfaction, suspicion, or scorn; never inside compounds. Almost always sentence-initial and followed by a comma or exclamation mark.
mistakes
Two readings of the same character: voiced 哼 (verb: hum, groan, snort) and toneless nasal 哼 (pure 'hmph'). Heuristic: if the character heads a verb phrase or a compound it's 哼; if it stands alone as a scornful exclamation it's 哼.
Left radical 口 - a small open square marking 哼 as a sound from the mouth: a hummed tune, a pained groan, a contemptuous snort. Anchors the vocal-sound family alongside 啊, 哈, 啦.
Right phonetic 亨 supplies the full sound with no drift. Its own meaning ('to prosper, to go smoothly') plays no role here - it is purely a sound marker. Same phonetic appears in 烹 (to boil). The high level tone fits the drawn-out nasal hum.
