The villanelle is a French poetic form consisting of five three-line verses and a sixth four-line verse. The first and third lines of the first verse are repeated alternately as the last line of the next four verses and then placed together as the ending couplet of the last verse. In addition, the five three-line verses all rhyme aba, with the last verse rhyming abaa. Thus there are only two rhymes in the entire poem. In most villanelles the repetition is light and graceful, but in some, including the most famous one, Dylan Thomas' "Do Not Go Gentle into That Good Night," the repetition is used to express powerful emotion.