"Slug" is a song by Passengers, a side project of rock band U2 and musician Brian Eno. It is the second track on Passengers' only release, the 1995 album Original Soundtracks 1. The track was originally titled "Seibu" and was almost left off the album before it was rediscovered later during the recording sessions. Though Eno made most of the creative decisions during the recording sessions, "Slug" was one of the few tracks that the members from U2 tried to craft themselves.

Lyrically, it is a portrait of a desolate soul during a time of celebration. As Passengers were writing songs for fictional soundtracks, they tried to create a visual suggestion from the music that was more important than the story within the lyrics. In "Slug", the instrumentation is intended to represent the lights turning on in a city at night. The group primarily drew inspiration for the song from U2's experiences in Tokyo at the conclusion of the Zoo TV Tour. "Slug" was praised as one of the best songs on the album by critics from various publications.

U2 and musician Brian Eno intended to record a soundtrack for Peter Greenaway's 1996 film The Pillow Book. Although the plan did not come to fruition, Eno suggested they continue recording music suitable for film soundtracks, as Eno did with his Music for Films album series. The result was Original Soundtracks 1, an album of ambient and electronic music, created as a side project between U2 and Eno under the pseudonym "Passengers". Vocalist Bono felt the visual suggestion from the music was more important than the story told by the lyrics, so the band tried to create visual music when recording, continuing a trend that had begun with their 1993 song "Zooropa". U2 spent time in Shinjuku, Tokyo, at the end of the Zoo TV Tour in 1993, and their experience in the city influenced the recording sessions. The vivid colours of the street signs and billboards reminded them of the set of the 1982 science-fiction film Blade Runner. Bono has said that Original Soundtracks 1 evoked the setting of a "bullet train in Tokyo".

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