Halloween is a time for us to face our fears and embrace the thrill of being terrified. Usually, this means dressing up in creepy costumes and watching lots of horror movies, but music, too, is full of scares. Realizing this, the good folks at Pandora set upon the intriguing task of cataloging and ranking the world's scariest songs. To do so, the data scientists behind Pandora's Music Genome Project studied thousands of tunes around areas including song construction, production, sounds and mood to determine their Top 10. Below, see the final list — which, perhaps, not surprisingly, includes such hair-raising artists as Nine Inch Nails, Tool and Lamb of God — and read on for our interview with Pandora data scientist Erik Schmidt and Director of Music Analysis Steve Hogan to get a deeper understanding of their methodology and conclusions.

10 Scariest Songs of All Time, According to Pandora:

Nine Inch Nails - "The Becoming"

Pixies - "The Happening"

Bauhaus - "Dark Entries"

Joy Division - "Transmission"

Lamb of God - "Contractor"

Tool - "Ænima"

Nirvana - "Heart-Shaped Box"

Korn - "Bottled Up Inside"

A Perfect Circle - "Thinking of You"

Whitechapel - "Eternal Refuge"

Video of The Becoming

I GUESS THE MOST OBVIOUS QUESTION IS HOW, FOR THE PURPOSES OF THIS LIST, DID YOU GUYS DEFINE "SCARY"? ISN'T IT SUBJECTIVE?

ERIK SCHMIDT, STAFF SCIENTIST, PANDORA Sure, it's subjective — what is scary for one person might not be for another — but we're using a few things to identify songs on the list. One is Pandora's Music Genome Project that leverages human-based analysis across 450 characteristics, such as instrumentation, genre and tempo. However, the biggest part of predicting what the mood of the song is actually through looking at how listeners interact with it.

We use more than 200 dimensions — or representations of a song we call embeddings — which allows our machine learning system to detect patterns that are informative of human emotions. But the reality is mood is a tricky signal to find in a piece of music. There are cultural aspects that come through when we have representations of how people listen to music. This is why we use machine learning and Pandora's expert curators to weigh in alongside data scientists to explore listener habits.

We looked at individual moods like anguished, distraught, eerie, harsh, menacing, spooky, tense, anxious and volatile, and the list is a representation of songs that scored the highest on this subset of moods.

CAN YOU TALK ABOUT THE VARIOUS PARAMETERS AND METRICS AS THEY APPLY TO A PARTICULAR SONG, PERHAPS?

SCHMIDT For each of the moods we talk about above, we have scores between 0-1, where 1 indicates the algorithm is 100 percent confident that this is anguished or eerie, and 0 means it is not.

For Nine Inch Nails' song "The Becoming," some of the top moods we identified include paranoid, bleak, gloomy, angry, ominous, confrontational and nihilistic. These characteristics are a result of the band's use of non-linear instrument timbres and effects, which humans are programed to find distressing.

IT'S INTERESTING THAT MAYNARD JAMES KEENAN SINGS ON TWO OF THE TOP 10 SONGS, ONE WITH TOOL AND ONE WITH A PERFECT CIRCLE. DO YOU THINK THERE'S SOMETHING PARTICULARLY SCARY ABOUT HIS VOICE AND/OR LYRICS?

STEVE HOGAN, DIRECTOR OF MUSIC ANALYSIS, PANDORA I think there are some carefully chosen studio reverb effects employed to accentuate the creepiness of his voice. He also has a talent for switching between a softer, more vulnerable vocal tone, to a more explosive, aggressive delivery that makes him sound like an unstable, slightly demented character!

Video of TOOL - Ænema

Video of A Perfect Circle - Thinking Of You

NINE INCH NAILS' "THE BECOMING" COMES IN AT NO. 1. WHAT MAKES THAT SONG PARTICULARLY SCARY?

SCHMIDT As noted [before], for "The Becoming," the top moods we identified include paranoid, bleak, gloomy, angry, ominous, confrontational and nihilistic. Some others are harsh, epic, manic and nocturnal.

HOGAN These facets contrast with the hushed and screaming vocals, which creates a suspenseful and unsettling mood. Melodically, this song makes use of an exotic-sounding scale, which features a major third but a flat second scale degree giving the song a dissonant quality.

HOW HARD WAS IT, GENERALLY SPEAKING, TO RANK THE LIST, AND HOW SLIM IS THE MARGIN ON SOME OF THE SONGS IN TERMS OF THEIR RANKING?

SCHMIDT Things are pretty crowded at the top of our most-scary metric. Looking at our data, we're looking at tenths of a percentage point. The Nine Inch Nails song registers a 6.2, the next one down — Pixie's "The Happening" — is a 6.06.

WHAT SONG COMES IN AT 11, AND WERE THERE OTHER SONGS THAT ALMOST MADE THE CUT AND THAT MAYBE THE TEAM HAD TO "FIGHT" OVER?

SCHMIDT When compiling the top songs, we took the highest percentage by each artist so we'd have a diverse list. The 11th unique artist and song would be "Reflect the Storm" by In Flames. Interestingly, if we grouped this list by artist, you'd find that Nine Inch Nails had a greater number of songs that scored highest according to our metric.

We talked with our curators about including the "Halloween Theme" by John Carpenter and "Superbeast" by Rob Zombie, because both are are strongly associated with scary vibes. However, both of the songs were further down the calculated list, so ultimately, we decided to go with the machine's analysis.

WERE THERE ANY SONGS THAT MADE THE TOP 10 OR MAYBE RANKED HIGH OUTSIDE THE TOP 10 THAT WERE SURPRISING TO THE TEAM?

HOGAN I was surprised to see the Joy Division song, "Transmission," so high on the list. This one defies the conventional wisdom that music needs to be in a minor key to sound scary. This song is harmonically very simple, and it oscillates back and forth between two major chords, D major, and C major.

WHAT, PERSONALLY, IS THE SCARIEST SONG YOU'VE EVER HEARD?

HOGAN Hands down, the most terrifying piece of music I've ever heard is a 1961 composition by Polish composer Krzysztof Penderecki called "Threnody to the Victims of Hiroshima." This piece is written for 52 strings, and is nearly 10 minutes of "nails on the chalkboard" dissonance. It triggers my primal fear response like nothing else I've ever heard. It has been used in David Lynch's Twin Peaks, and also in Wes Craven's 1991 horror film The People Under the Stairs.