scratch and find

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.
See also: and, find, scratch