Where, in India, to knock the first couple of nails! (5)

I believe the answer is:

patna

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But I can't explain it at all! Could you help me understand?

(Other definitions for patna that I've seen before include "Rice town" , "Long-grain rice type" , "Variety of long-grain rice" , "Source of long-grain rice" , "City of savoury rice" .)

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