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の裏を

the back/underside of ~; outwit ~

→ の
phrase Rare #42,241
the back/underside of ~; outwit ~ の裏を literally means “the back or underside of ~.” In 裏を掻く, it is part of an idiom meaning to outwit someone or act contrary to their expectations.
JA: 机の裏を見てみて。
EN: Take a look under the desk.

電気スイッチの裏を見てみろ

Take a look behind the electrical switch.

— 善き人のためのソナタ (2006)