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to wriggle; to squirm; to crawl like a worm
暗闇の中で何かが蠢いた。
Something wriggled in the darkness.
池の底でゆっくりと生き物が蠢いている。
A creature is slowly squirming at the bottom of the pond.
石をめくると無数の虫が一斉に蠢くのを見た。
When I lifted the rock, I saw countless insects wriggling all at once.