socks and knocks
 n.pl.— «Readers should understand clearly that if the power industry prevails in its court challenges to the initiative, the huge amount of money expected to be spent primarily on reducing what the industry commonly calls “socks and knocks” might not get spent. (“Socks and knocks” is a word play on the symbols for sulfur dioxide and nitrogen oxides, SO2 and NOx, respectively.)» —“Cleaning Up With ‘Socks and Knocks’” by Bill Paul Motley Fool Apr. 21, 2005. (source: Double-Tongued Dictionary)

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