A few weeks back, the Internet went a little crazy over an image of a gorilla. In the photograph seen above, an imposing gorilla stands squarely before the camera, his brow furrowed. The alpha male, named Akarevuro, cocks his arm back with a clenched fist. Moments after the image was taken, the gorilla punched the photographer.

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"Normally, they timidly avoid visitors when they move close, but not this time," the injured party, veteran wildlife photographer Christophe Courteau, told Caters News Agency. "Akarevuro was too excited and drunk." Corteau claimed that on that particular day, Akarevuro and his family, who live in forests of Rwanda's Volcanoes National Park, were drunk on bamboo, which is a staple of the gorilla's diet.

"The gorillas are just mad about the bamboos at this time of the year, stems and roots," Courteau said. "The problem is, when the gorillas eat too much of these bamboos, there's a side effect: fermentation." Effectively, Courteau claimed, the gorillas' stomachs act as self-sustaining distilleries, turning fibrous bamboo into alcohol. Outlets like Boing Boing and io9 picked up the story, with headlines proclaiming that the gorilla was drunk.

There's only one hitch to the tale: It's impossible for a mountain gorilla to become intoxicated from eating bamboo.

"The suggestion that these gorillas were drunk from fermenting bamboo in the stomach is misleading," says Joanna Lambert, a professor of biological anthropology at the University of Texas at San Antonio. "They just don't have that kind of stomach."

The stomach of a gorilla is like the stomach of a human, in that it is full of digestive acids. It contains no fermenting bacteria, making it impossible for fermentation to occur within the stomach itself. As in humans, fermentation can occur in a gorilla's large intestine, but even that wouldn't render a gorilla drunk. According to Lambert, the process is a completely different kind of fermentation than the one that produces alcohol.

A more plausible scenario is that the gorilla was on a sugar high. Some foods, like bamboo, can contain lots of sugar, which translates to more readily available energy when consumed. If the gorillas had eaten a lot of bamboo, Lambert says, they might have appeared more energetic than usual, but they definitely weren't drunk.

"Somebody needs to tell me why, if they get drunk on bamboo stems, they don't get drunk on any of the rest of their vegetarian diet," says Sandy Harcourt, professor emeritus in the anthropology department at the University of California, Davis.

Drunk animals in the wild are rare. "There are all kinds of 'forest legends' of animals like elephants getting drunk, and for the most part that's not happening," Lambert says. An exception can be when a fruit drops from the parent tree and begins to ferment due to yeast on the outside of its skin—that would make the fruit mildly alcoholic. "But that's a completely different kind of system," Lambert says, "and that's not what's happening [in the photographs]."

So what did cause the gorilla to punch the photographer? Most likely, the visitor was simply getting too near the gorillas. "The tourists just got a bit too close and didn't respond to behavioral cues," Lambert says. "The silverback was doing what he should do, which is to be vigilant and get rid of strangers." When a gorilla feels threatened, it will often let an interloper know by puffing its lips or emitting small vocalizations. Ignore those warnings, and the alpha male might take more drastic action.

Despite the photographer's unfortunate run-in, Lambert emphasizes that tourism has been hugely beneficial to gorilla conservation. "Gorilla tourism is phenomenally important to local economies," she says. "It's overwhelmingly one of our success stories of conservation, both in Rwanda and Uganda." But tourism isn't without its drawbacks, which manifest when people push too close to the wildlife.