"Knockout" is a song recorded by the British pop/rock group Triple 8 in 2003. It was released as a single on 21 April 2003 in the United Kingdom. The single debuted at a peak position of number 8 in the UK Singles Chart.

"Twins (Knock Out)" is the debut single by Super Junior, when they were still known as Super Junior 05, which was released online as a digital single on November 8, 2005 and later on the group's first studio album, Twins on December 5, 2005.

Before the single was released for download, Super Junior 05 made their debut as a group on SBS's Popular Songs on November 6, 2005, performing "Twins (Knock Out)".

Super Junior 05's version kept the original song's hip-hop influence but incorporated heavier bass elements and quicker rap, forming the song into a rap rock piece. The promotional title of the song, "Twins", was added to the song's title to mark the change in lyrics from the original song. The Korean lyrics, written by Yoo Young-jin, speaks of self-deception and the indecisive aspects of mind, contrasting the feelings between a man towards love and how he has to decide whether or not he should continue to love or fight with sticking to his own destiny.

The rest of the tracks in the digital single are less emphasized in the rap rock genre as "Way for love" is a bubblegum pop track and "Over" and "L.O.V.E" are purely mainstream pop tracks with a light R&B vibe. The group's first ballad, "You Are the One" heavily emphasizes gentle harmonization and R&B.

The music video was filmed in a dance studio. A majority of the scenes are simply dancing footage, where the members are surrounded by fire and also the contrast, blue sky.

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