look as if butter wouldn't melt in (one's) mouth

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look as if butter wouldn't melt in (one's) mouth

To appear innocent or reserved in certain company, when in fact one may have the opposite demeanor. Sure, he looks as if butter wouldn't melt in his mouth when he's around people he doesn't know, but stay a while and you'll see what he's really like.
See also: butter, if, look, melt, mouth

look as if butter wouldn't melt in one's mouth

Fig. to appear to be cold and unfeeling (despite any information to the contrary). Sally looks as if butter wouldn't melt in her mouth. She can be so cruel. What a sour face. He looks as if butter wouldn't melt in his mouth.
See also: butter, if, look, melt, mouth