Toxic

Toxic was written by Cathy Dennis, Henrik Jonback and the production team Bloodshy & Avant, Christian Karlsson and Pontus Winnberg, who produced it. It was written with Janet Jackson in mind and offered first to Kylie Minogue, who turned it down after hearing a snippet in the record company offices. Minogue later said it was like the fish that got away and that you just have to accept it. It was recorded at Murlyn Studios in Stockholm and Record Plant in Los Angeles, and mixed by Niklas Flyckt at Khabang Studios in Stockholm.

The hook samples Tere Mere Beech Mein, from the 1981 Bollywood film Ek Duuje Ke Liye. Surf guitar runs underneath, at 143 beats per minute in G minor, and the lyric treats a lover as a dangerous and addictive drug. Spears chose it as the second single over (I Got That) Boom Boom and Outrageous, calling it an upbeat song that is really different. It was released in January 2004, peaked at number nine on the Hot 100 on 27 March 2004, and reached number one in Australia, Canada, Ireland, Norway, the UK and several other countries. It won Best Dance Recording at the 2005 Grammys.

Pitchfork's Rob Mitchum placed it third on the best singles of 2004 and wrote that "finally, she just acted like an adult." In 2009 Pitchfork's Jess Harvell put it at number 141 among the tracks of the decade, calling it the last great Britney single so far and describing the backing track as a club-tempo stepping breakbeat colored by James Bond soundtrack outtakes. Joseph Kahn directed the video, in which Spears plays a secret agent who poisons her boyfriend. It cost 1 million dollars, her most expensive to that point, and premiered on MTV's Making the Video on 13 January 2004.