describes a person with a "poker face" or having no expression at all
Definitions (粵典–words.hk)
形容詞
冇乜反應、表情 dull; expressionless; with a poker face; literally: wooden mouth wooden face
佢個人好呆板,幾時都木口木面。
佢个人好呆板,几时都木口木面。
keoi5 go3 jan4 hou2 ngoi4 baan2, gei2 si4 dou1 muk6 hau2 muk6 min6. She's very dull and her face is always expressionless.