A terrible thing did not happen in the White House press room on Wednesday. In a sudden non-attack in front of a roomful of non-horrified witnesses, CNN reporter Jim Acosta did not lunge at, strike or place his hands “on a young woman just trying to do her job as a White House intern.” It would be a very bad thing if that had happened. But it didn’t. So that’s good.

You would not know this, however, if you believed a statement released by White House Press Secretary Sarah Huckabee Sanders, claiming that the attack occurred (which, once more, it didn’t) or, worse, if you saw the edited video she tweeted out purporting to show the incident unfolding.

Significantly, this version of the clip, which was taken from the live broadcast of the full, heated exchange between Acosta and President Donald Trump, wasn’t altered by just anyone with iMovie. It was the handiwork of YouTube personality, conspiracy theorist and accomplished web troll Paul Joseph Watson, editor at large for the conspiracy site InfoWars and former contributor to the radio show of über conspiracy hustler Alex Jones. Together, Watson and Jones have peddled such non-peer-reviewed notions as the danger of chemtrails and the approach of the New World Order. So, not exactly Peabody Award-winners here.

Perfectly reasonable people could have perfectly reasonable disagreements about whether Acosta was merely engaging in vigorous questioning or had crossed the line into hectoring — a disagreement that is hardly without precedent in the long history of White House press conferences. What made Wednesday’s incident different was not just that the Watson video is deceptive, and that the White House Press Secretary then trafficked in it. More troubling was how easily the edited footage gained believers, and how deftly it played on the ways the human brain makes distinctions between what’s true and what’s not.

The complete clip of the Acosta-Trump dust-up runs two minutes and forty-three seconds, but the relevant moment comes just before the minute and a half mark, when Acosta is speaking and a White House intern appears to surprise him, approaching from the side and below (she was crouching on the floor nearby) and reaching to grab the microphone. A brief tangling of arms ensues, Acosta is heard saying, “Pardon me, Ma’am” in a level voice, and the intern withdraws. The Watson video runs 15 seconds, eliminates the context, and opts instead for an extreme close-up, repeatedly showing a moment when Acosta’s hand makes contact with the intern’s arm.

Watson, according to The Washington Post, calls any allegation that he edited or changed the speed of the video to make it look more abrupt or violent a “brazen lie.” But he did admit to BuzzFeed that “digitally it’s going to look a tiny bit different after processing and zooming in.”

Elizabeth Loftus, professor of law and social psychology at the University of California Irvine, isn’t buying it. “The videos are totally different,” she says. “Somebody is pretty talented to do it that skillfully and fast. They made it look like he hit her, that he reached out his arm and made contact.”

Loftus knows a thing or two about manipulated evidence and biased perceptions. An authority on human memory and its exceeding imperfections, she has been an expert witness in multiple celebrated cases, including the McMartin preschool molestation case and litigation involving Michael Jackson as well as the Duke University lacrosse players. Her TED talk on memory has garnered more than a million views. In the case of the Acosta footage, she says, the altered video leverages not just the way our perceptions of what we’re seeing can be manipulated, but the way our political biases can turbocharge those manipulations.

In a paper Loftus co-authored in the Journal of Experimental Social Psychology in 2013, she and her colleagues showed 5,296 volunteers doctored photos of five ostensible news events that did not in fact occur, and asked the volunteers if they remembered hearing about them or seeing them on the news. On average, 27% of the subjects reported that they had indeed seen the pictures — which they could not have — but the results were heavily skewed by political orientation. People who disapproved of George W. Bush, for example, were likelier to “remember” having seen a picture of him vacationing at his Texas ranch with then-Houston Astros pitcher Roger Clemens during the Hurricane Katrina disaster; he did not. People who disapproved of Barack Obama were similarly more inclined to think they recalled a picture of Obama shaking hands at the United Nations with then-Iranian President Mahmoud Ahmadinejad. That never happened either.

“People are more gullible consumers of information that supports their political views than of information that challenges them,” says professor of psychological science Peter Ditto, also of the University of California, Irvine. “Psychologists call this ‘motivated reasoning.’ Trump has weaponized this basic human tendency by repeatedly offering his supporters alternative accounts of events that confirm their beliefs.”

The President, in fairness, by no means invented this technique, or was the first to use it in a calculated way. Loftus has seen manipulation of memory and perception play out repeatedly in criminal trials, when witnesses are merely questioned in suggestive ways, and their stories change accordingly. “I’ve also studied suggestive psychotherapy that leads people to believe they had childhood experiences they didn’t have,” she says.

Video evidence certainly can be of value both in a courtroom and in other contexts, but only if it’s used honestly. Attorney and professor David Paul Horowitz, who teaches the Electronic Evidence and Discovery Workshop at Columbia University School of Law and who viewed both the original Acosta video and the one shared by Huckabee Sanders, does not think Watson’s creation would last long in a courtroom.

“The objection to the White House clip would likely be that the repetitive loop of a very short clip would be prejudicial, and serve only to inflame the fact-finder,” Horowitz wrote in an email to TIME. “The objecting party would likely request that the video be replayed, in its entirety, each time the jury wanted to see it, so that the entire context of the contact would be presented.”

Of course, inflaming viewers was an intended feature of the clip, not a bug. For a known purveyor of conspiracy theories to create it was bad enough, but promoting it with the full authority of the White House takes it to another level. “The possibilities,” says Ditto, “are chilling.”

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Write to Jeffrey Kluger at jeffrey.kluger@time.com.