Great summary of the video from here:

"The clip for her sing-songy "The Bells" was filmed in one continuous take in the heart of the suburbs: under floodlights on a football field in the middle of the night. Over the course of an impeccably choreographed few minutes, Lowell shares the screen with an undead street gang, a roller derby team, a squad of cheerleaders, a marching band, and a few ancillary people in shimmering bodysuits. There's an undercurrent of menace through the whole thing, with unexplained gashes on many characters, and Lowell lazily swinging a baseball bat throughout. By the end, it seems that she may have beaten the viewer to death."
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Lowell on her inspiration:
"I love horror movies. Obviously there are more intellectual reasons for liking horror movies than others; I like them for the cheap thrill. This one in particular I used Carrie as an inspiration. "
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"I wanted it to be one take, and for every moment moving forward to give you the idea that there was going to be something more, and for you not to have any idea what that thing was going to be.

I liked the idea that because the song is so serene in its own way, using visuals that were a little unsettling to go with them. It gives a different take on my vocals, because they're already so nursery rhyme and simple, so if you have that underlying thing in it that's a little creepy, it almost adds to the creepiness of the song. "