Welcome to Science of the ScareEvery month I will dissect a Big Science Question from a horror movie and talk through it in (mostly) easy-to-digest terms.

Science and horror have a wild, entangled history and have left us with loads of questions to ponder. Deep, important questions like: just how many ways could we have a zombie pandemic? Is genetic engineering always a slippery slope to monstrosity? This month’s Big Science Question:

Could you make a human head explode using only sound?

Exploding heads are a fun (and usually goopy) horror staple. By the laws of horror movie physics, we know that the human head can explode thanks to vibrations. These vibrations can be psionic, as most famously depicted in Scanners (1981) or Rubber (2010), or they can be sonic. Some of the most memorable sonic head explosions are in Freddy’s Dead: The Final Nightmare (1991) when Freddy (Robert Englund) rips out Carlos (Ricky Dean Logan)’s hearing aid and replaces it with a parasitic one that lethally amplifies sounds so that knives on a chalkboard aren’t just annoying, they’re skull-shattering; and in The X-Files episode “Drive” (1998), where Mulder (David Duchovny) is abducted by a driver (Bryan Cranston) who is trying to escape a building pressure in his head caused by prolonged exposure caused extremely low frequency (ELF) waves emitted from a U.S. Navy experiment. Vince Gilligan, who wrote the episode, was partly inspired by real U.S. military experiments with radio waves. It sounds silly, but if we can make wine glasses shatter with screams, couldn’t we also make heads crack apart if only we find the right sound?

The reason why wine glasses shatter, of course, is because every material has resonant frequencies at which it naturally vibrate. The wine glass won’t crack for any scream or operatic singing — the pitch of the sound has to be matching the resonant frequency of the glass in order to get it to vibrate, too.  In last month’s Science of the Scare, I discussed how exposure to vibrations near a resonant frequency of the human eyeball can cause it to deform and produce “haunting” visual disturbances. Others have described what’s referred to as vibroacoustic disease, conditions where long-term exposure to infrasound (0-20 Hz) and very low frequency noise (20–500 Hz) messes with the structural integrity of the body’s tissues and cell signalling. Most of us aren’t dealing with extreme exposures to these frequencies, though; we may sit through a two-hour horror movie with near-infrasound laced into the soundscape, but those sounds won’t shake our cells around.

 

 

The idea behind Gaspar Noé using near-infrasound in the disturbing first half-hour of Irréversible (2002) and Paranormal Activity (2007) apparently sneaking infrasound into its found footage franchise is that even though we don’t necessarily perceive these extreme bass frequencies as sound, we are still capable of experiencing them in other ways. Some people experience low frequencies as more of a sensation of pressure or unease, which, when coupled with terrifying imagery, might serve to heighten horror. The horror movie context is important here: I’ve been listening to a loop of low-frequency audio on YouTube while writing this piece and I’m not getting any ghostly vibes. Mostly what sounds I can perceive are kind of annoying.

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Context aside, vibration isn’t the only important ingredient to the low frequency experience. Intensity is also an important factor. So, if you’ve ever turned on a Gaspar Noé film at home, expecting to feel the discomfort of the near-infrasound that he’s incorporated into his works, you might be disappointed, especially if you don’t have a sweet surround sound system with the volume cranked up. The infrasound experience in film, like any sound design, is really mixed for when you have your butt parked in a theatre seat.

 

“[…] if you did tweak to the right frequency, directed it to the right part of the skull, and played that frequency with major volume and intensity, you might have some luck […]”

 

As an aside, low frequencies aren’t the only sounds that can affect us. If your ears are young or sensitive enough, you may have already had strange experiences with high frequency sounds, often referred to as mosquito tones. In the mid-00s, some stores who were tired of teenaged loiterers installed devices that emitted high frequency sounds that would deter youths but otherwise be unnoticeable to older shoppers whose hearing had lost sensitivity to that high-frequency range. The sounds weren’t necessarily harmful to most people — hypersensitivity issues aside, mostly exposure felt like an annoying pressure inside your ears, but the devices were capable of being set to unsafe volumes. Generally speaking, prolonged exposure to sound above 70 decibels can damage your hearing, and exposure to 120 decibels or more can cause immediate hearing damage. Some of the mosquito tone devices could be cranked up to 104 decibels.  As far as I know, popularity for the device has sort of died off.

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Alright, so, we know that certain frequencies can bother us, but where are the brain explosions? To get tissues to vibrate, we’d have to find their specific resonant frequencies, and then blast those frequencies in a very directed and intense way at the tissues. This is basically what we do with shock wave lithotripsy, a medical procedure where we use ultrasound waves to break up kidney stones into smaller bits. Here’s where we hit our first snag: you’re trying to explode a head, which is made up of so many different types of tissues, from rigid bone to stretchy skin; from flexible cartilage to gelatinous eye goo (aka the vitreous humour); from fibrous muscle to soft and squishy brain matter.

 

 

Each of these tissues has different frequencies at which they’ll naturally vibrate… so which one are you going to target? And even if you choose one tissue that seems promising like, say, the skull, because a good amount of research has been done on sound frequencies and skulls in terms of bone-anchored hearing aids, and because it seems like if you can get the skull to shatter, its brittleness might make a mess of some of the softer tissues at the same time. Well, if you did tweak to the right frequency, directed it to the right part of the skull, and played that frequency with major volume and intensity, you might have some luck as long as you’re patient (you’ll have to wait for the target tissue to vibrate and deform for quite a while before something happens). Your luck improves if the skull has some flaw or weak point that we can exploit — even glass shatterers recommend using cheap, flawed wineglasses, since the deformations from vibrating are more likely to crack the glass at those weak points.

I assume that the sound-shattered skull probably won’t look much like a Scannersesque eruption of brain and guck. There’s still skin and scalp to hold everything relatively together. Generally, sonic weapons are not super efficient beyond blowing out eardrums or being disorientingly loud, but that hasn’t stopped military and police forces from exploring sound as a way to incapacitate or even kill. So, could we see a head-exploding sonic weapon in the future? Maybe, but it’s not somewhere I’d like to see us throwing research funding and efforts. I’d rather this particular gore effect remain firmly in the realm of unreality, thanks.

 

How do you feel about infrasound — is it spooky or overrated? Have a Big Science Question from horror that you’d like to see answered? Let us know over on TwitterReddit, and in the Horror Movie Fiend Club on Facebook!