The interjection 哼
An interjection (感叹词) is a word or expression that occurs as an utterance on its own and expresses a spontaneous feeling or reaction. It expresses feelings and emotions but does not name them. It is usually placed at the beginning of a sentence.
哼 
may express:
1) groaning in pain: “оuch!”, “оh!”.
may express:
1) groaning in pain: “оuch!”, “оh!”.Examples
哼，好痛苦！
Ouch! So painfull!
hēng, hǎo tòngkǔ
哼！我什么时候会感觉好点？
Oh! When I will feel better?
hēng! wǒ shénme shíhou huì gǎnjué hǎo diǎn
2) dissatisfaction or anger. It is often used in response to a threat, and can be translated as “um”, “uh”, "heck".
Examples
哼，我再也不理！
Heck, I won’t pay attention to it anymore!
hēng, wǒ zài yě bù lǐ tā
哼，难怪她没有来
Uh, no wonder she didn’t come.
hēng, nánguài tā méiyǒu lái
哼，有什么做不到的呢？
Heck, what are we not able to do?
hēng, yǒu shénme zuòbudào de ne