From the Fyre festival documentaries to Dan Mallory’s bestselling con, scams are having a moment. On HBO’s Last Week Tonight, John Oliver looked into a less headline-worthy stream of scams: psychics, particularly on daytime TV.

Oliver was adamant that his segment would not interrogate whether or not psychics are “real” – “For one, they’re not,” he panned. And while it’s easy to dismiss psychics (“fun, too”), Oliver argued that it’s foolhardy to ignore their influence in America; according to the Pew Research Center, four in 10 Americans believe in them. “Statistically, that means that out of all the people who saw John Travolta’s Gotti movie, four of them are psychics,” Oliver said.

It’s not a surprise, then, that psychics have built a multimillion-dollar industry that is “larger and grimmer” than one might assume, propped up by daytime TV shows and pseudoscience.

Oliver admitted that mediums, or people who claim to communicate with the dead, do make “compelling TV”. But while “watching people tear up can seem incredible, the techniques that psychics use to achieve those moments are significantly less incredible”.

Oliver looked into two main methods: cold reading and hot reading. Cold reading involves narrowing high probability guesses into a broad, generalizing claim. “It’s like asking a room full of praying mantises: ‘Has anybody here lost a loved one because you ate them after having sex?’” Oliver explained. “You know that all those little green hands are going up.”

The secret is that “the broader the generality, the higher the chance it resonates with someone” – basically, it’s “a magic trick, and yet prominent, smart people are willing to cosign on psychics’ abilities”.

For example, Oliver turned to a Today show clip from a couple years ago, in which Matt Lauer expressed amazement at Hollywood Medium’s Tyler Henry’s “vision” of fishing with his dad.

“Look, maybe Tyler Henry genuinely accessed the afterlife, an action which would fundamentally change our understanding of everything on earth,” Oliver said following a clip of Lauer telling a similar vision to Larry King years before. “Or maybe he just googled ‘Matt Lauer Dad’ and hit the fucking jackpot”.

That technique – guessing with research – is known as hot reading. But whatever the method, Lauer fell for it.

“You can see why people are vulnerable to psychics,” Oliver conceded. “A message from a lost loved one is something many people in the midst of grief would do anything for.” However, though psychics may think they offer a harmless coping mechanism for grief, “at best, it is reckless for a stranger to take a stab at ventriloquizing the dead. Loss is complicated, and mourning doesn’t look the same for everyone,” Oliver said.

“But at worst, when psychic abilities are presented as authentic, it emboldens a vast underworld of unscrupulous vultures, more than happy to make money by offering an open line to the afterlife, as well as many other bullshit services,” he continued. Even worse, “TV actively enables this ghoulishness” by granting psychics an air of validity in questionable or damaging circumstances; Oliver used the example of Amanda Berry, a kidnapped girl who watched, in captivity, as a psychic on a daytime talkshow told Berry’s mom that she was dead.

Oliver argued that the host, Montel Williams, deserved some blame in this mess: “If Oprah interviewed a live alligator and it ate four members of her audience, I’d be angry with the alligator, but I’d also be kinda angry with Oprah.”

In sum, Oliver said, we should be wary of how pop culture validates psychics, because “every time a psychic makes a grieving widow cry on Dr Oz, 10 con artists get their wings”.