hēng​hēng

to groan

哼哼 hēng​hēng
to groan
To groan or moan due to illness or physical pain; to make low sounds from the nose.
to hum
To hum or croon softly.
hrumph
(onomatopoeia) The sound of snorting or hrumphing.
to murmur
To speak in a very low voice or mutter, especially while dreaming or half-awake

Frequency

Movie subtitles
2.80 per million appears in 1% of films
Written text
8.43 per million

Sources