Ask any comic and they’ll tell you that the cardinal sin of comedy is stealing someone’s joke.

On Wednesday, a video surfaced accusing Amy Schumer of doing just that, comparing her stand-up sketches and bits from Comedy Central’s Inside Amy Schumer to similar jokes by other comics, including Wendy Liebman, Kathleen Madigan, Tammy Pescatelli, and the late Patrice O’Neal.

The video was removed from Vimeo (which, like The Daily Beast, is owned by IAC) on Thursday after Viacom, which owns Comedy Central, claimed copyright infringement. (Viacom did not respond to requests for comment by the time this story was published.)

Schumer defended herself on comedian Jim Norton’s Sirius XM radio show in a nearly hour-long special episode that aired Wednesday night.

“I will take a polygraph test and put it on my show this season,” she said, adding that she had never seen or heard any of the bits that were posted in the video, and that “both Kathleen and Wendy know me and they don’t believe I would do that.” (Norton is a longtime friend of Schumer and previously came to her defense in October, when she was first accused of stealing O’Neal’s jokes.)

Schumer said she didn’t believe the accusations were “personal,” but that “people build people up and then they like to rip them down because they’re experiencing some success.”

She’d asked to go on Norton’s show, she said, because she wanted to clear her name—“because more than anything I want credibility as a comic… I don’t think comedians can forgive joke-stealing… I’m not going to become one of those people who is known for taking other people’s jokes. I’m the fattest, ugliest, monster with the stinkiest vagina—keep writing that. But don’t call me a joke thief.”

Indeed, comedians don’t easily forgive joke thieves. Carlos Mencia was blacklisted from the comedy world after Joe Rogan, a fellow comic, confronted him about plagiarizing during a 2007 set at the Comedy Store in Los Angeles.

Rogan had previously called him out for lifting other comics’ material in a 2005 blog post, but after the 2007 video went viral, people began posting clips of Mencia’s bits next to those of other comics, much like the Schumer video.

Mencia’s joke theft was particularly egregious: He copied an infamous bit from Bill Cosby almost word-for-word, mimicking Cosby’s delivery and using the exact same punchline.

Denis Leary’s career was never the same after he was accused of stealing jokes from Bill Hicks and Louis C.K.

Dane Cook suffered from similar accusations (and also alleged that Steve Byrne stole his “essence”), though not as mightily as Leary and Mencia. Robin Williams was also thought to have lifted other comics’ material.

“People stopped doing their acts when he would come in [to the Comedy Cellar] because they were worried he might lift something,” Pete Dominick, host of Sirius XM’s Stand Up! With Pete Dominick, told The Daily Beast of Williams. Dominick, who knows Schumer from the Comedy Cellar when they performed there before she became famous, doesn’t think she stole from anyone.

“Comedians aren’t inclined to steal not because it will necessarily ruin their careers, but because they want the respect of other comedians,” he said. “[Amy] paid her dues. She got into all the clubs. She’s a comic’s comic. She’s fucked a lot of people, but she hasn’t fucked anyone over.”

Sam Morril, another comic who met Schumer at the Comedy Cellar, agreed: “Amy is not a thief,” he wrote in an email. “She is a special comic who cares about comedy. Also, if there’s a Trainwreck 2 and they’re looking for a swarthy looking Jew, I am available!”

Dave Rubin, a comedian who hosts an online political talk show, doesn’t know Schumer but saw video and didn’t think the comparisons were particularly obvious.

“The cadence of the Wendy joke is similar, but I don’t think there’s any evidence she necessarily stole it,” Rubin said. “If what Amy said is good enough for Wendy, then it’s certainly good enough for me,” he added, referring to Liebman’s latest tweet in defense of Schumer, attributing their similar bits to #greatminds #parallelthinking.

Around the time the video posted, Liebman commented in a now-deleted tweet: “Amy Schumer doing 1 of my best jokes on her HBO special.”

Pescatelli has also deleted a series a tweets regarding Schumer and the video: “What has always been amazing to me is that she purports to be a feminist and yet only steals from other female comedians,” she wrote. “If we call her on it we are ‘jealous’ or career-shamed. Be successful. WE want you to do well, just do it with your own material. BTW she blocked me.” (Schumer claimed on Norton’s show that she’d blocked Pescatelli because she was “unkind” to Rachel Feinstein, a comedian and Schumer’s good friend).

On Thursday, Pescatelli apologized to Schumer, again via SiriusXM’s Opie and Jim Norton program, for accusing her: “It went too far, and for that I’m super-apologetic.” Schumer had “every right to be mad,” Pescatelli added.

A lot of jokes in comedy are derivative. They’re mined from universal experiences like sex, love, parenting, family—which is why comics have to work particularly hard to distinguish themselves.

The Schumer video raises questions whether we can ever be sure of the originality of a joke. Dominick said we can.

“There’s an unwritten rule at the Comedy Cellar that any comic who becomes a father has to watch all of Ray Romano’s material, because he’s already done all the parenting jokes,” Dominick said.

“All stand-up comedy has a premise and a punchline,” he added. “The situation is what’s specific, and your own vulnerability, your own honesty.”

Or, as Rubin said, “The one and only thing that every comic agrees on is that you do not steal jokes. It’s a lot easier to steal now because comics just tweet jokes that are often the genesis of what’s going to become a much longer bit. I’m doing stand-up much more sparingly now, but when a funny one-liner comes to me I’m hesitant to tweet it because I know someone could do it in a club.

“I remember working with this guy who was lifting ideas from everyone. He justified it as ‘parallel evolution.’ I thought, ‘If you could only put that kind of creativity in your jokes.’”