We had been expecting rain and were dressed accordingly: ankle-high waterproof hiking boots topped with gaiters to prevent the mud from seeping in over the top, quick-drying pants and shirts, rain ponchos, hats. Having walked and then climbed over swamp, heath, and bamboo forest, through stinging nettles and giant ferns, we were indeed covered in mud almost up to our knees, but the sun, despite last night's predictions of torrential downpours, was now shining, and I felt as though I were on the set of the 2006 version of King Kong, in the scene where Naomi Watts, having befriended Kong, surveys his world with him from a narrow mountain shelf. We were all perched, no less precariously, on an almost 90-degree volcanic slope—not solid ground underfoot but layer upon untold layer of springy, slippery roots and other vegetal matter. One of our guides had just tumbled head over heels for about ten yards before being able to arrest his fall. The scene below us was storybook, or cinema, perfect: small villages dotting the gentle hills, a bright early-morning haze suffusing the green valleys. The northern Rwandan province of Musanze (formerly Ruhengeri) is particularly lush and fertile and swathed in life-giving mists. In the distance was the string of the other six Virunga volcanoes, each wreathed in its own dreamy coronet of clouds.

"Get down," Eugene, our guide, hissed suddenly, interrupting my reverie. We were being charged by a female in Guhonda's group. It happened in a split second. I'd been vaguely aware of her feeding off to our right, uphill. Suddenly, she was headed toward us at a gorilla gallop. I saw nothing more, because I was concentrating on keeping my eyes on the ground, remembering the instructions we'd been given the night before by a gorilla expert from the Dian Fossey Gorilla Fund, whose research station, Karisoke, is right nearby: Don't scream when stung by stinging nettles during the climb up the volcano, lest you alarm the gorillas (some of us had been stung, and had obediently suppressed screams); when charged, do not make eye contact and, above all, do not run away.

It was over as suddenly as it had begun. We'd acted appropriately. Our guides launched into gorilla-speak, making grunting noises meant to convey contentment. Were we in danger? Probably not. Mountain gorillas (fittingly for the King Kong legend that they inspired when they were first "discovered" by a European scientist in 1902) have the moniker "gentle giants," and their displays of anger are supposedly just that—displays, mock charges. But one cannot be utterly sanguine. Although these gorillas are habituated—meaning used to seeing humans—they are nevertheless wild creatures. We are in their world up on the volcano and need to play by their rules. If our situation was not actually dangerous, it was at least not entirely predictable. Tensions had flared—and then just as quickly had dissipated. For now.