In Joe and Anthony Russo’s Captain America: Civil War, the world’s mightiest superheroes battle it out over the Sokovia Accords, which would compel the independent Avengers to become a federal force. One of the major issues at play is Captain America’s (Chris Evans) support for his best friend Bucky Barnes (Sebastian Stan) when he’s blamed for a major act of terror. Barnes, after all, operated as the HYDRA assassin Winter Soldier, and it sure looks like he was responsible for the massacre in question.

Warning: The following content contains spoilers for Captain America: Civil War.

Here’s the rub: Bucky didn’t do it. New Marvel bad guy Helmut Zemo made a doppelgänger do it. A fresh take on comic book villain Baron Zemo played by Daniel Brühl, Helmut obtained HYDRA/S.H.I.E.L.D. secrets following Black Widow’s info dump at the end of 2014’s Captain America: The Winter Soldier and uses it to turn the reclusive Bucky into his puppet of chaos. Bucky becomes the wedge in Zemo’s complex plan to split the Avengers apart, and for the most part it works.

But how can Zemo control him when Bucky could crush him with his robotic pinky? Simple: Trigger phrases. Using one of HYDRA’s most top secret and valuable info inside a leather-bound red notebook, Zemo learns to make the Winter Soldier obedient and vulnerable to “orders.”

Post-hypnotic suggestion is a phenomenon when hypnotized subjects — such as Bucky — are compelled to act when awakened by “triggers” such as specific words or phrases. That’s what those random, innocuous words like “Homecoming” (a slight nod to next year’s Spider-Man movie) were all for. Zemo was basically saying passwords to access the killing machine lying dormant in Bucky.

The trigger phrase is a part of the Winter Soldier in Marvel Comics but it’s exaggerated in Civil War. In Ed Brubaker’s Captain America books (which the Russos have said on numerous occasions heavily influenced them), the Red Skull uses the “one time” shutdown phrase “Sputnik” to render Bucky unconscious.

Is the science behind post-hypnotic suggestion real? Some of it is valid, but it’s never been really in favor with the scientific community — and on an anecdotal level, most Google search results are more in line with hokey self-help pages and stage performers. But comedian Stephen Fry once recalled getting through a daunting Saturday Night Live musical sketch by consulting a hypnotist. The hypnotist “triggered” Fry to relax after he says his line, “Play it, bitch.”

But whatever the science, it’s a rich literary device seen in countless TV shows, movies, and yes, comic books. Tony Stark references The Manchurian Candidate in Civil War, and in Avengers director Joss Whedon’s 2005 film Serenity, a similar scenario occurs where River Tam is “triggered” watching a candy commercial.

So that’s what’s going on with Bucky in Civil War. It’s made explicit in the film and in fact matches up the comic pretty earnestly. But even if the science may be a bit hokey, Captain America: Civil War is a movie where a frozen World War II soldier and a billionaire genius in armor fight over whether or not they should be legal. Writing in faux psychology is the least implausible thing.

Photos via Marvel, YouTube.com/Marvel Entertainment