Sentence:  [H]is words were grave, his manner was earnest, and his speech came from the fulness of his heart. If there had been a <WSD>false</WSD> note, a false look, Harry would have detected both. 
Meaning of the word marked with <WSD> tags:  In a remark or narrative, an indication (as discerned by the listener or reader) of untruth, insincerity, or inconsistency.