Rupert Grint says Shia LaBeouf ''got naked and kept seeing this owl'' on the set of their new film.

The 'Harry Potter' actor has confessed his 'The Necessary Death of Charlie Countryman' co-star took his preparation for the role very seriously, resulting in him ''smashing up'' the set and behaving erratically.

Quizzed on whether Shia, 28, did lots of mad things on the set of the film - for which he admitted to taking acid for scenes in which his character takes ecstasy - Rupert said: ''Er, yeah. Yeah, he did. I guess you'd call him a method actor. He kind of lived that part.

''It was ... interesting. I think he's talked about it a bit himself. Things happened which I probably shouldn't go into.

''He smashed the place up, got naked and kept seeing this owl. If anything will make you not do drugs, it's watching that.''

The 26-year-old actor admitted, however, that Shia's character wasn't the only one to be involved in strange scenes in the upcoming film.

He explained to The Guardian newspaper: ''I'm a wannabe porn star called Boris Pecker. My main plot is I take too much Viagra and require medical assistance. So it's me running around with a strap-on.''

Meanwhile, Rupert has also revealed he's bought a pet tortoise named Madeline to help him get over his homesickness since moving to New York.

He said: ''I named him before I found out his gender. You don't really need to do anything with him. He doesn't even need water that often. Doesn't like to be touched either.''