sb looks like butter wouldn't melt in his/her mouth
释义
idiomsb looks like butter wouldn't melt in his/her mouth(also butter wouldn't melt)used in order to say that someone looks very kind and good, even though they are not:From the look of her, butter wouldn't melt in her mouth.He speaks very quietly, and you'd just think butter wouldn't melt, but you have to watch out for him.