Sentence:  She twisted her hands behind her; but all the knots held good. / She <WSD>writhed</WSD> her hands till her fingers were wet with sweat or blood. / They stretched and strained in the darkness, and the hours crawled by like years, / Till, now, on the stroke of midnight, / Cold, on the stroke of midnight, / The tip of one finger touched it! The trigger at least was hers! 
Meaning of the word marked with <WSD> tags:  To contort (a part of the body).