Third-person singular present tense of befoul; causes something to become foul or contaminated.
Simple conjugation of 'befoul' with the '-s' ending for third-person singular present tense.
Even in modern English, 'befoul' is standard enough that 'befoul/befouls/befouled/befouling' conjugates automatically—readers understand it immediately, unlike many other 'be-' words that feel distinctly archaic.
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