If you've ever watched South Park, or spent a little too long on the Internet, at some point you've probably heard tell of the Brown Note. You may be surprised to learn that several scientists have actually looked into it, to see if it might be real.

For the uninitiated, the Brown Note is a hypothetical sound that causes anybody who hears it to instantly and uncontrollably defecate themselves without warning. Around the Internet, there are tales of this being weaponized, of DJs accidentally playing the Brown Note and making an audience of 500 crap themselves, and of people testing out audio equipment only to look down and discover it's brown trouser time.

It's not clear what the origin of the urban myth is – and it is an urban myth – though there are a few candidates. One was a story published in New Scientist in 1974, about a "lost" Victorian instrument called the Giant Collophone. According to the story, a humungous instrument was to be played in front of an audience, including Prince Albert. When the first note was sounded, however, "the audience showed signs of discomfort, which gave rise to panic before a verse of the anthem was complete. Moreover, the evident mass psychological disturbance was accompanied by unpleasant physiological symptoms - pain, diuresis and diaorrhoea."

The article was satirical, but has been mistaken for true. Which is understandable, given how weird everything was back in Victorian times anyway.

_See.

Another possibility is that the legend stemmed from stories about the Republic XF-84H aircraft, which is possibly the loudest plane in existence. The aircraft, nicknamed "Thunderscreech", was notorious for giving crew headaches and, reportedly, nausea. Crucially though, there is no mention of anybody spontaneously crapping themselves.  

So, what does the science say about the Brown Note? Well, various researchers have looked into the possible effects of infrasound (low-frequency sounds that humans cannot hear) on humans. 

"Reported effects include those on the inner ear, vertigo, imbalance, etc.; intolerable sensations, incapacitation, disorientation, nausea, vomiting, and bowel spasm; and resonances in inner organs, such as the heart," one review of the literature from 2001 reads.

The evidence for such effects is, it's fair to say, mixed. There is plenty of evidence for people becoming annoyed by infrasound, or having sleep disturbances.

"Drivers of long-distance transport trucks exposed to infrasound at about 115 dBA had no statistically significant incidence of fatigue, yawning, sleepiness, vertigo, tinnitus, headache, subdued sensation, hearing impairment, abdominal symptoms, or hypertension," one study read. "Exposure to about 115 dBA of infrasound has no effect on humans."

^{The Mythbusters also looked into the brown note.}

Another review that looked at the potential use of sound as a weapon couldn't find anything solid either.

"Evidence for bowel spasms and uncontrolled defecation is even scarcer. Among all the literature surveyed for this article, the only hint found was one on 'digestive troubles' observed during experiments with a strong 16-Hz siren," the review reads.

"These were, however, not specified at all, and the explanation immediately following talked of objects vibrating in clothing pockets. 158 in the low frequency exposures up to 150 dB no bowel spasms were observed. The same holds for low-frequency animal experiments. Here it is noteworthy that also in reviewing vibration experiments no mention was made of bowel spasms or uncontrolled defecation."

"Thus, it seems that these alleged effects are more based on hearsay than on scientific evidence. It cannot be excluded that at higher sound levels in specific frequency ranges, vomiting, uncontrolled defecation, or heart problems will occur, but the evidence for them is scant at best."

Essentially, despite humans having been subjected to an incredibly wide range of notes, none of them have been brown. It's possible (though not likely) that there is a magical note out there that will make you crap yourself, but no real evidence for it yet. And if there was such a note, do you not think we'd have found it by now?