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| English | Russian |
| he knows how to do his stuff | он знает своё дело |
| know one's stuff | знать своё дело (быть компетентным специалистом: If someone knows his/her stuff, it means the person is very knowledgeable and skilled in that area – This carpenter really knows his stuff because he has 30 years of experience. Bullfinch) |
| know stuff | знать что-либо назубок |