'Harry Potter' fans are ever eager to learn more about what happened behind the scenes of the movie series. But perhaps we were better off not knowing this one.

The latest comes from Potter himself, Daniel Radcliffe, as he recalled filming the movie 'Harry Potter and the Philosopher's Stone'.

The actor was interviewed as a part of the "Hot Ones" series on the Youtube channel First We Feast.

The video (at the time of writing) is closing on 4 million views on Youtube.

Host Sean Evans asked Radcliffe what he could remember from shooting a particular scene in the first 'Harry Potter' movie.

It depicts tranfiguration teacher Professor McGonagall (Maggie Smith)'s classroom full of animals.

After "debating whether to tell that story", Radcliffe said: "They must've had upwards of 60 there," recalling the number of animals on set.

But one little guy stood out.

"I don't imagine they were often all on set together," the actor continued, "but definitely in that scene – in the transfiguration classroom – there was a monkey of some kind in a cage that just started jerking off relentlessly."

He said they "were very well-behaved" apart from that.

Except for one other moment Radcliffe then remembered.

"I think Rupert [Grint] maybe got peed on by a bat at one point as well," he revealed.

Watch the full interview below.