"Knives Out" features electric and acoustic guitars, complemented by singer Thom Yorke's haunting vocals. It appears on Radiohead's 2001 album Amnesiac, and was also released as that album's second single, receiving more radio airplay than the band's other songs of the period.

The song was developed during the 18-month Kid A and Amnesiac sessions, and it is legendary for supposedly having taken 373 days to record. According to Yorke, "We just lost our nerve. It was so straight-ahead. We thought, 'We've gotta put that in the bin, it's too straight.' We couldn't possibly do anything that straight until we'd gone and been completely arse about face with everything else, in order to feel good about doing something straight like that. It took 373 days to be arse-about-face enough to realise it was alright the way it was." Although "Knives Out" is not similar to Radiohead's earlier rock style as featured on The Bends (1995), it is usually noted as one of the most traditional guitar pop songs the band has done this century.

"Knives Out" was played to Johnny Marr (The Smiths), by guitarist Ed O'Brien, who was touched when told that the track was heavily influenced by his former group. The tune's chord progression is also very similar to the one heard in the first part of Radiohead's 1997 single "Paranoid Android." "Knives Out" was later covered by The Flaming Lips, on their Fight Test EP. The song was also covered by classical pianist Christopher O'Riley on his album True Love Waits, and on jazz pianist/bandleader Brad Mehldau's most recent album, Day is Done.

Yorke has usually described the song as being about "cannibalism." In one interview he said: "It's partly the idea of the businessman walking out on his wife and kids and never coming back. It's also the thousand yard stare when you look at someone close to you and you know they're gonna die. It's like a shadow over them, or the way they look straight through you. The shine goes out of their eyes."

A promotional video was directed by Michel Gondry. It features Thom Yorke in a hospital by the bedside of a woman, played by Emma de Caunes, who appears to be his partner in the video. The whole video was shot in one take, quite remarkable considering the scene changes required. Attempts to interpret the surreal imagery and fit it with the song lyrics were dashed when Gondry eventually revealed that the video was autobiographical. Some may find thematic parallels with Gondry's later film Eternal Sunshine of the Spotless Mind. The "Knives Out" video is not included on a popular DVD compilation of Gondry's music videos and short films.