From Longman Dictionary of Contemporary Englishput your finger on somethingput your finger on somethingCORRECTto know or be able to explain exactly what is wrong, different, or unusual about a situation There was something about the man that worried Wycliffe, but he couldn’t put his finger on it. → finger
Examples from the Corpus
put your finger on something• One child put her finger on 17.• Ezra put his finger on the photos.• Lord Wyatt had put his finger on it: The hunts wouldn't let her in.• The Captain of the Lymington-Yarmouth ferry could not quite put his finger on what was wrong.• But what they were she could not quite put her finger on.• Nightbreed almost does, but fails for some reason I can't quite put my finger on.• Something was happening amongst the youth movement that so admired him and he couldn't quite put his finger on it.• I can't put my finger on it, but there's something different about you.• I can't put my finger on it. 