A river cruise is like a movie. The boat glides from scene to scene, the travelers get to know each other, and around the final curve awaits resolution, or perhaps revelation.

Or at least that's how the voyage proceeds in Colombian director and co-writer Ciro Guerra's fascinating The Embrace of the Serpent. Nominated for the best foreign-language-film Oscar, the Amazon-set drama is a trip in more ways than one. It intertwines two journeys of discovery, inspired by the real-life journals of German ethnologist Theodor Koch-Grunberg and American ethno-botanist Richard Evans Schultes.

Both are looking for a rare plant, although for different reasons. In 1909, Theo (Jan Bijvoet) is seriously ill, and his semi-Westernized native guide (Miguel Dionisio Ramos) believes yakruna will save him. The men seek a young shaman, Karamakate (Nilbio Torres), who mistrusts white people and believes himself the last of his tribe. Only when Theo says he can reconnect Karamakate with his surviving kin does the healer join the expedition.

Some 30 years later, Evans (Brionne Davis) follows Theo's path. The American has been recruited to find new sources of rubber for his country, at war with a Japan that controls Southeast Asia's sticky sap. Evans is an expert on hallucinogenic plants and hopes to find yakruna. He enlists an older Karamakate (Antonio Bolivar), who believes he has lost his memory, and perhaps even his identity.

Karamakate's wisdom mingles the practical, the ecological, and the mystical. To him, shooting stars become totemic animals, including the jaguar and the boa, which impart wisdom in dreams. He laughs, a generation apart, at Theo and Evans' attachment to their possessions. He's also amused by Theo's songs, although suitably awed when Evans' gramophone emits Haydn's "The Creation."

Such devices, which include the compass Theo loses to a village chief, are the white man's magic. They are potentially corrupting, since they may supplant the local knowledge and cause even a shaman to forget who he used to be.

During the two quests, several episodes justify Karamakate's contempt for European explorers and exploiters, who've oppressed indigenous peoples in the service of both rubber and Jesus. A stop at an orphanage run by a lone monk is as chilling an illustration of the white man's jungle madness as Aguirre, the Wrath of God. And when Evans and Karamakate arrive at the same mission three decades later, the place has descended into a nightmare worthy of Apocalypse Now.

Theo and Evans each lug cameras into the Amazon basin, and David Gallego's cinematography honors the period by being black-and-white — but crisp and widescreen, very unlike the vintage glass-plate photo in which Karamakate is confused to glimpse a version of himself. The elegant monochromatic compositions also contrast a short full-color sequence near the journey's end.

Yakruna is a (fictional) plant used to make a brew that summons vomit and visions. It's not clear that it can cure Theo's exotic illness, but perhaps it can rectify Evans' scientific detachment.

That may be Guerra's goal for the viewer as well. The Embrace of the Serpent, whose title is a metaphor for psychedelic experience, isn't as flamboyantly nutty as such hippie-era Latin perplexities as Alejandro Jodorowsky's El Topo. But it is bewitchingly strange, and as enveloping as the Amazon jungle.

Indeed, the place itself is transformative. To embrace the serpent may be to digest strange dreams, but an overhead shot of the terrain ultimately suggests another meaning. From above, it's clear that the river coils through the forest like an endless snake.

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