When it comes to Harry Potter secrets, Daniel Radcliffe doesn’t monkey around.

The actor’s appearance on the Hot Ones YouTube series on Thursday started out innocently enough, with the Boy Who Lived chowing down on wings while talking about his new movie, Escape from Pretoria. But it wasn’t long before the chamber of secrets was broken wide open.

Besides asking about food highlights and lowlights on Harry Potter, host Sean Evans pointed to a scene in The Chamber of Secrets where Professor McGonagall (Maggie Smith) is teaching transfiguration in a classroom filled with animals, and asked Daniel what he remembered from that day.

Well, Daniel remembered it vividly. Though perhaps “remembered” is the wrong word. The story seemed scarred into his psyche, like the lightning bolt on Harry’s forehead.

There was a monkey masturbating on the set of Harry Potter.

Daniel considered holding back the story, but finally began: “You asked about such a specific thing in that McGonagall classroom. I definitely remember that there was a — there were a lot of animals, first of all, to address that part of the question. They must’ve had upwards of 60 there. I don’t imagine they were often all on set together, but definitely in that scene in the transfiguration classroom, there was a monkey of some kind in a cage that did just start jerking off relentlessly.”

He continued: “But generally speaking the animals were very well behaved. Although I think [Rupert Grint] maybe got peed on by a bat at one point as well, but yeah, I got away pretty cleanly after that.”

Daniel’s monkey story almost seems too bananas to be true. But, sure enough, if you search online, there appears to be a moment that made it into the movie involving a monkey, or perhaps a mandrill … going off script.

And that, everyone, is why you never, ever open the Chamber of Secrets ― especially if there’s a monkey in there. 

Watch Daniel’s answer in the video above around the 8:20 mark.