scratch and find
scratch (something) and you'll find (something else)
If you investigate a certain type of person, organization, or thing closely, you will almost certainly find another, often contrary characterization or trait as well. There is a misbelief in popular culture that if you scratch a devout Catholic, you'll find a radical fundamentalist. My father always told me, "Scratch a successful business, and you'll find a hive of corruption."
scratch a — and find a —an investigation of someone or something will soon reveal their true nature.
The first version of this expression used in English, in the early 19th century, was a translation of a remark attributed to Napoleon: grattez le Russe et vous trouverez le Tartare , ‘scratch the Russian and you will find the Tartar’.
1924 George Bernard Shaw St Joan Scratch an Englishman and find a Protestant.