Here's a fun parlour game to play with your (inebriated, adult) friends: Pull out a smartphone with "safe search" disabled, and try disproving the 34th rule of the Internet. Rule 34, according to long-standing legend, goes something like this: If it exists, or can be imagined, there is Internet porn of it.
Tetris blocks? Yep, absolutely.
Leprechauns? The Web's got it.
Robots? Aliens? Goats? Trombones? Buck up and Google them.
As bemused players have gradually been finding, however, there is a new catch in the game: It may actually be more difficult to find porn of everything/anything now than it had been previously.
In the 13 years since a British teenager first coined the term "Rule 34," Internet consumption patterns and the online porn industry have changed.
Alien goat sex may still exist somewhere in the Internet's unplumbable depths, but it is far deeper down than it used to be.
"I think we're seeing the death of Rule 34," sighs Ogi Ogas, a computational neuroscientist at Harvard and the author of the first large-scale study on Internet porn. "It's out there, if you want to find it. But it's not easy anymore."
Ogas conducted his study - an analysis of more than 55 million pornography searches - in 2009 and 2010, at the tail end of the period that may go down in history as the golden age of Rule 34.
Like the mainstream media during that same period, the porn industry was experiencing some major turbulence, thanks to the Internet.
Home computers and faster Internet speeds liberated consumers from the awkwardness of interacting with an inquisitive mailman or video-store clerk, which meant they could chase down whatever flavor of smut they wanted. And thanks to the same technologies that were fueling these cool new things called "Web logs," just about anyone with an Internet connection and a willing audience could produce it.
The thing that gets me about online porn is that it's not that wild. It's explicit, and some of it is extreme. But it's oddly very narrow. I wouldn't describe it as diverse or creative.
There are few good censuses of porn sites from this time, alas: Even Ogas's study looked at what users searched for, and not what they actually encountered. But some earlier "netporn" researchers described a branching constellation of increasingly niche sites arrayed around every conceivable sexual identity and interest: "No theme is remote enough," one pair of researchers said in 2007. "No fetish too exotic."
Whether or not they realised it, those academics were just echoing a British teenager who had come to similar conclusions a few years before: In 2005, the then "16-ish" Peter Morley-Souter had chanced upon some Calvin & Hobbes erotica and turned it into a widely circulated Web comic.
"Rule 34," the caption reads. "There is porn of it. No exceptions."
But Morley-Souter, now 27 and using a slightly different name to avoid association with his famous law, has to admit that much about porn and the Internet changed in the 10-plus years that followed.
In the late aughts, just as Ogas was wrapping up his study, the online porn industry began consolidating - moving away from individual producers and distributors, and toward massive, crowdsourced aggregators called "tube sites." To give you an idea exactly how massive these sites are, consider this: Online porn comprises an estimated 4.7 percent of all desktop Internet traffic, and tube sites funnel the vast majority of that.
Much like YouTube, from which they are derived, tube sites such as Xvideos (the 23rd most popular site on Earth) and Pornhub (the 37th) allow just about anyone to publicly upload just about anything.
That infamously includes pirated porn stolen from websites that charge for the videos; this practice has gutted portions of the porn economy.
[Pornhub is] democratising the distribution of adult video content like YouTube did with general video content.
Piracy has hit small producers and distributors particularly hard, says Shira Tarrant, the author of the new book "The Pornography Industry." The sites making Calvin & Hobbes erotica or literal Tetris porn are, not coincidentally, the same ones that cannot afford a full-time, anti-piracy staffer.
Equally damning, from a Rule 34 perspective, is the fact that tube sites centralize power and influence in the hands of a single corporation - something that most casual consumers do not realize.
Eight of the 10 largest tube sites, including Pornhub, RedTube and YouPorn, are owned by MindGeek, an "information technology firm" headquartered in Luxembourg. And MindGeek, leveraging its vast, centralized troves of content and user browsing data, has dictated exactly which sorts of porn become and stay popular.
Most tube sites recommend and promote specific tags, for instance, which helps determine how we talk about sex.
They also decide what content to promote and what to bury, not unlike Amazon.com or Netflix. On top of its curated homepage (viewed by nearly 30 million people a month), and its carefully strategized media and social-media presences, Pornhub personalizes its content recommendations based on algorithm, which tends to smooth out any quirks or curiosities that people may bring to it.
"The thing that gets me about online porn is that it's not that wild," Tarrant said. "It's explicit, and some of it is extreme. But it's oddly very narrow. I wouldn't describe it as diverse or creative."
In a statement, Pornhub's vice president, Corey Price, denied that tube sites had any role in standardizing or mainstreaming online pornography: Porn is more diverse than ever before, he said, and Pornhub in particular is "democratizing the distribution of adult video content like YouTube did with general video content."
Nobody had come close to predicting the range of sexual tastes and interests.
But what limited data we have, at this point, suggests differently. In one of the most recent quantitative analyses of online porn, a team of five French researchers at several different institutions scrapped the metadata - including tags describing content - of 1.7 million videos on the popular tube sites Xnxx and xHamster. They found that, while an extraordinary range of material does technically exist, a mere 5 percent of the sites' available tags cover 90 percent of their videos.
The quote-unquote creative stuff, on the other hand, exists in backwaters too obscure to be found even by Google search.
In some regards, this new arrangement is not too surprising; if anything, it may better mirror the bell curve of contemporary human taste. Back in 2009, when Ogas started studying Internet porn, he was initially floored by the diversity and open-endedness of searches:
"Nobody had come close to predicting the range of sexual tastes and interests," he said. But while the range may have been huge, Ogas quickly discovered that the average was generally what you would expect: conventionally attractive, heterosexual people, having vaguely adventurous, heterosexual sex.
In other words, it may have appeared as if the Internet unleashed a flood of heretofore untapped sexual expression. But in fact, the people propping up Rule 34 were mostly just ... dabbling.
"If you Google 'skeleton porn' or 'sexy funeral director' or 'erotic stories about lumpy potatoes' you will find results," Ogas wrote in his 2011 book "A Billion Wicked Thoughts," which resulted from his research. "But most of us aren't spending our time looking for this stuff."
Leonard Delaney can, unhappily, confirm that: He is the creator of that Tetris erotica you have heard so much about. Delaney has written and self-published more than a dozen novellas with names such as "Conquered by Clippy." A few of them have gone quite viral, but he still averages only $100 in sales each month.
Does Delaney think Rule 34 is defunct? Frankly, he is not sure.
At first, he told The Washington Post, it struck him as "mathematical certainty" that the rule becomes more true over time, because people are constantly producing new porn and new erotic stories. But on second thought, he is not sure that stuff is new - it could just retread old subjects and themes.
Delaney, for one, is determined to keep the law alive: His most recent story is about Microsoft's racist chatbot, Tay. He has ambitions of writing erotica about slinkies and cul-de-sacs one day.
But Delaney's white whale remains Rule 34; he does not think there is any porn about the law itself. And until that exists, he rightly observes, the whole debate is academic.