Plural of flagellate; multiple whip-tailed organisms, or third-person singular verb meaning to whip or beat.
From flagellate (to whip, or whip-tailed organism) + -s (plural or verb conjugation).
Interestingly, when you say 'she flagellates,' you could mean either the biological act (swimming with flagella) or the painful one (whipping with a whip)—same word, wildly different contexts.
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