"Bellyache" is a song by American singer and songwriter Billie Eilish. The song was released on February 24, 2017, through Darkroom and Interscope Records. It was written by Eilish and Finneas O'Connell, with the production being handled by O'Connell.

In an interview with Eve Barlow of Noisey, Eilish said

"It's obviously fictional. When me and my brother are writing we find it fun to put yourself into character or become someone else, to write about something we've never done before. 'Bellyache' is about the concept of guilt, when you do things in the moment because you feel so strongly about them. In the end you're left with the decision you made. That line—'I thought that I'd feel better, but now I gotta bellyache'—is about how you kinda know that you're the worst but you don't care. It's about a psychopath who regrets being a psychopath but doesn't really care."

During an interview with Billboard, Eilish also stated

"It's really fun to put yourself into a character—into shoes you wouldn't normally be in. You don't have to be in love with someone to write a song about being in love with someone. You don't have to hate somebody to write a song about hating somebody. You don't have to kill people to write a song about killing people. I'm not going to kill people, so I'm just going to become another character."

Mike Wass of Idolator called it a "sinister synth-anthem that positively seethes fury and frustration".Billboard's Jason Lipshutz said "she wrapped the macabre lyrics around a delectable pre-chorus hook and a steady acoustic pattern that eventually gives way to a sizzling drum machine. She knows that a song like 'Bellyache' is going to get her more sideways glances than Top 40 airplay, and that's fine with her." Estelle Tang of Elle labeled it a "banger about bad decisions".Pigeons and Planes's Jacob Moore stated that the song "shows off an intriguing edge, which is in large part due to the fact that this is a song about murder".

The music video, directed by Miles and AJ, was released on March 22, 2017. Sydney Gore of Nylon described the music video: "Her latest Miles and AJ-directed visual for 'Bellyache' shows her stranded in the middle of a deserted highway. At first, the scene seems innocent as Eilish drags a little red wagon containing what appears to be some personal belongings. Shortly after, we find out that she's loaded with garbage bags full of cash. When the chorus hits, we feel compelled to dance along with her in the majestic mountain tops and almost forget that there's something fishy going on. It's almost like we're experiencing hallucinations as we watch her bust out some sick choreography down the road which leads to the great unknown. We won't spoil the ending for you, but it's got a major plot twist that we did not see coming at all. So what does it all mean? Clearly, Eilish is not one to be underestimated."

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Wikipedia