Source: Disney Plus/Marvel Studios

Last week, the new hit sitcom WandaVision revealed to its many fans [spoilers ahead] that Kathryn Hahn’s character Agatha was the big bad. The show did that with an infectious song that immediately swept the internet and then got stuck in everyone’s heads, like it or not.

Fans are known for being passionate about the things they love and spending a lot of time thinking about those things, but they often don’t think much about the impact of the music in their favorite shows and films. That music is an integral part of telling the story and why those stories resonate — and there’s some psychological research behind that.

In the case of "Agatha All Along," the impact was so striking that the song went viral, with one fan posting a YouTube video revealing that part of the music had actually been playing in various sitcom themes on the show since the start, in a kind of meta hint as to what was coming. That analysis of the recurring motif caught the interest of both fans and the show creators, eventually prompting WandaVision composers Robert Lopez and Kristen Anderson-Lopez to take to twitter to corroborate YouTube poster Artsy Omni’s sleuthing.

Kristen Anderson-Lopez tweeted: If you are wondering why you were so ready for the last song, it’s because you were hearing the same song week after week.

“Agatha All Along” is intentional in its musical composition in more than one way. In an interview with Indie Wire, the composers (who are also responsible for another song no one can get out of their heads, Disney’s “Let It Go”) said that they were trying to remind viewers of classic fan-favorite sitcoms from "I Love Lucy" to "The Partridge Family," and also to bring a feeling of impending darkness. They accomplished this by using a tritone, sometimes called “the Devil’s interval”, which creates a sense of creepiness that runs underneath the outwardly cheery tune. The composers then varied the meter and tone and instrumentation to create different versions of the telltale motif.

While this is one of those few times that fans are all talking about the music of their favorite show, a television show’s composers are always critical collaborators in telling the story that fans are enjoying. Music elicits powerful emotions in humans, sometimes creating emotions we might not have felt otherwise as we watch our favorite shows. Music can either intensify, dampen, or maintain our emotional experience. That’s because we hear music as an emotional expression and unconsciously construct a representation of that emotion, in a form of emotional contagion. As music psychologist Patrick Juslin put it, “You may know that what you hear is ‘just music,' but the mechanisms that evoke your emotions do not.”

Music is used in several ways in film and television. The musical score can be used to add to a scene’s intensity, create pathos, or serve as a cue to the audience that something bad is coming — as in the reveal of Agatha. Variations in the instruments used and the timbre and tempo of the music create different emotions in the listener. For example, descending notes are mostly perceived as sad and ascending notes as happy, but changing the instrumentation changes the feel of the music. Higher-pitched and more staccato instruments like the marimba evoke joy, whereas cello and saxophone convey sadness and fear. The piano appears to be the most neutral instrument, which means that the manner in which it is played has a significant impact on listeners’ emotional response. In multiple WandaVision episodes, the recurring motif is played in the various theme songs in different ways.

How does music create emotional reactions? There are several cognitive mechanisms involved, most of which occur in the older part of the brain known as the limbic system, so the reactions are automatic. If you have ever experienced music that “gave me chills," that distinctive sensation is associated with limbic system activity. Neuroimaging studies show that the brain interprets certain aspects of music, such as an accelerating pace or sudden changes in rhythm or volume, as a signal that we need to pay attention. Humans have evolved to recognize such changes as meaningful since survival might have depended on the ability to notice patterns in sounds in order to know when to make a quick escape! When the rhythm of a piece of music changes, heart rate and breathing change in someone listening. So manipulating aspects of the music of a television show or film produces different emotional responses in viewers.

Learning is also involved in our response to music. The composers’ intentional evocation of familiar sitcom themes from the past adds to the impact of the music in WandaVision. Both being a fan and listening to music can result in “absorption” or “engagement," an intense focus on something that can alter emotions or ways of thinking. Sometimes called “flow,” absorption results in a loss of self-consciousness when something has captured our attention completely, to the extent that we feel immersed in whatever we’re watching or doing. This experience is generally pleasurable, resulting in changes in the frontal cortex and the release of the neurotransmitter dopamine. The effect is even greater when the music is personally meaningful, something which the familiarity of the music from WandaVision, reminding us of beloved sitcoms of the past, may have inspired.

Finally, having Agatha herself (actress Kathryn Hahn) sing the vocals for “Agatha All Along” added another increment of familiarity. The combination of subtle priming with the repeated motif, the manipulation of tempo and timbre and instrumentation, and the undeniably catchy tune itself have left many fans with a persistent (if not entirely unwanted) earworm.

If it’s now in your brain after reading this post, you’re welcome.