groan : 侧重指因受到难忍受的精神负担或强烈的痛苦等而发出沉重的呻吟，也指显示强烈不满的叹息声。
- We could hear the groans of the wounded soldiers.
- He looked at the piles of dirty dishes and gave a groan of dismay.
- to groan with pain/pleasure
- He lay on the floor groaning.
- We all groaned at his terrible jokes.
- They were all moaning and groaning (= complaining) about the amount of work they had.
- He moaned with pain before losing consciousness.
- "Let me die," he moaned.
- Thelma's always moaning (about something), and forgets how lucky she actually is.
- "I don't like potatoes," he moaned.
- First she moans (that) she's too hot, and then that she's too cold.
- After a lot of moaning and groaning, they eventually started work.
sigh : 多指无意识地发出表示沮丧、悲痛、悔恨或厌倦等情绪的深沉叹息。
- She sighed deeply and sat down.
- "I wish he was here," she sighed (= she said with a sigh).
- He leaned back in his seat with a sigh.
- "Ah, you're here," she said and heaved/let out/gave a sigh of relief.
sob : 指抽噎声或呜咽声，或边说边哭。
- I found her sobbing in the bedroom because she'd broken her favourite doll.
- You're not going to help matters by lying there sobbing!
- I could hear her sobs from the next room.