This post discusses the events of the April 9 episode of “The Americans.”

'THE AMERICANS': Nina (shown above) faces the threat of a FBI polygraph test at 10 p.m. on FX. -- Nina (Annet Mahendru) faced down a polygraph, and won, in the April 9 episode of “The Americans.” (Credit: Patrick Harbron/FX)

“You have no armor, nothing to protect you — except your wits, your courage, and your beauty. How is it possible you’re here?” Oleg tells Nina during their celebratory tryst after she beats the FBI’s polygraph and earns an even deeper level of Stan’s trust. “You are an amazing woman.”

He might as well have said Nina is an amazing machine, just like the lie detector she beat and the devices Phillip Jennings learns about that make the Arpanet possible — not to mention the video game console Henry Jennings sneaks out to play with. Like all of the rest of the technology in this episode, Nina is remarkably advanced, even if her capabilities are not yet clear to everyone who thinks they know how to use it.

When the episode “Arpanet” begins, the lie detector seems like the most intimidating technology the characters will have to deal with. In a chilling opening scene, Oleg, who has danced back and forth between seeming like Nina’s enemy and her protector with the same deftness as the gospel preachers he admires so much, promises Nina that he can help her beat the polygraph. Only when she is out of the room does Arkady ask whether he was bluffing her, and Oleg admits that beating the test is merely a “possibility,” rather than an actual scientific certainty.

But as the episode progresses, and Oleg talks Nina through every trick she can think of, from clenching parts of her body to visualizing him in the room at key moments, the polygraph recedes in our imagination. It may have intimidating wires and Velcro straps, but the machine starts to feel like a cheap prop in comparison to the body itself. That does not drain the tension from a moment toward the end of the interrogation when it seems like Nina may have flubbed the question “Are you pretending to be an FBI informant when in fact you’re spying for the Soviet Union?” But when Nina passes, with the help of the cool, white corner of the room where Oleg told Nina to envision him, she seems stronger than at any point in the series, a woman who has mastered her body and the games that several very dangerous men are playing with her.

The polygraph seems even more insignificant as “Arpanet” cuts back and forth between Nina’s preparation and interrogation and Phillip’s latest mission, to bug the technology of the title. As Nina is being trained to beat the lie detector, Phillip is talking to a professor to learn what, exactly, the Arpanet is and does — and then killing a scientist who gets in the way when he tries to extract data from it.

At a moment when explanations are in vogue in policy journalism, “The Americans” offers up a terrific, clear metaphor for what was, in the timeline of its show, almost inexplicable technology.

“You’re familiar with the Post Office?” the professor tells Phillip. “Let’s say you have a friend in Japan named Hirohito. Hirohito lives in a tiny, remote fishing village in Japan, and he wants to send you a postcard. But Hirohito only knows Japanese, and well, you don’t read Japanese. So he sends his postcard to the Japanese post office, which translates the postcard into a universal post office language.” “And is the post office in Japan?” Phillip wants to know. “Japan. Johannesburg. Bangkok. Rio. Anywhere and everywhere,” the professor tells him. “It’s sort of like God, without the big beard and the flowing white robes.”

While Oleg and Nina can figure out how to beat the lie detector, Phillip and Charles — an alcoholic asset Phillip activated for this mission — cannot even reckon with the Arpanet. When the professor describes “an endless ribbon of virtual highway,” Phillip, who is stuck on the metaphor, wants to know, “Going where?” When the man tells him, “The future?” the idea is abstract behind his comprehension. Charles is invigorated by the strangeness of it all, telling Phillip that the Arpanet is “the end of science fiction. Or the beginning of it. Playing with reality like it’s Silly Putty.”

But Phillip is more cautious, perhaps because he has some experience with what happens when you push an exciting new machine to its limits. “What was the point?” Phillip asks Charles, about the man he killed during the bugging. “For some X’s and O’s on a virtual highway? I don’t even know what that means. Do you know how many people I’ve killed? I mean, looked into their eyes and watched them die?” Charles, the futurist, sees only the glory of Phillip’s functionality. “It’s what you do,” he tells Phillip. “And you do it so very well.”

Nina may be exultant in her sense that she is operating at peak capacity, that she has gone to war with a piece of sophisticated technology and won. But Phillip, in bugging the Arpanet, has seen the moment when functionality seeks to be glorious and morally neutral and becomes something ugly instead.