（表示犹豫不定、沉思等）嗯，呃
Um is used in writing to represent a sound that people make when they are hesitating, usually while deciding what they want to say next.
例句
She felt her face going red — 'I'm sorry Rob, it's just that I'm, um, overwhelmed.'
她感到自己的脸变红了——“对不起，罗布，我只是，呃，一时情绪失控。”