The echoing double-voice of half-man, half-alien symbiote Venom was achieved “all at the same time” during filming instead of post-production, Eddie Brock actor Tom Hardy shared with EW.

“Actually, the sound boys, [Patrick Anderson on sound playback and production sound mixer Michael B. Koff], they worked relentlessly to trigger [it] — I’d have to lay down the vocal for Venom in the morning and then play Eddie opposite in my earpiece, and whoever was working in the scene with me, had to hear Venom at the same time but then ignore that they’d heard Venom,” Hardy said.

“And whenever I gave my cue line as Eddie Brock — this might not make any sense to anybody who’s not really techie and geeky about things like this like me — but Patrick would be under the stage queuing Venom accurately so I could cut across him and talk and argue with myself, and stuff like that. It’s a bit techie, it was fun. It was really, really good fun, and the sound boys, actually, to be fair, probably really play Venom. It’s my voice [laughs], but they play Venom.”

“It’s a real testament to Tom’s talent [because] he had to play these two characters simultaneously, and watching him manage both these personalities in his head at one time, just as a director, was so fun to see him acting literally opposite himself. It’s really impressive,” added director Ruben Fleischer.

Hardy, who pulled double duty as identical twin brothers Reggie and Ron Kray in 2015 gangster drama Legend, would act opposite himself through the use of vocal recordings and a double, making for a not-as-complicated-as-it-sounds “Tetris puzzle.”

“It was more of the same stuff, when I did the Kray twins in Legend, that was again audio record of the brother who was gonna cause the most amount of damage in the room, so I would act the one who does the least amount of damage but then predict the damage that was coming, but the vocals had to be laid down before we set the scene,” Hardy explained.

“Which means all the other actors had to know what the person in the room was gonna do, who wasn’t in the room when we filmed it, and then we put a double in there, so it’s a little bit like some kind of Tetris puzzle. It’s very geeky [laughs]. But I really enjoyed it, and no, it’s less complicated than it seems.”

It works swimmingly, Hardy said, “as long as I’ve got the guideline in my ear.” On set, outwardly talking to himself mirrored the affliction that befalls investigative journalist Eddie Brock, who becomes a twitchy and paranoid-looking weirdo after bonding with the mysterious extraterrestrial goo known as a symbiote.

“It looks weird from the outside if you don’t hear what I’m hearing. It just looks like a man talking to himself, which is partly Eddie Brock’s problem, really, for a lot of the transference of the symbiote into him,” Hardy said.

“And that’s what makes it a little bit quite funny, really. We see this poor guy struggling, talking to himself, and that’s what the crew really saw for four or five months is this poor guy — well, not so poor guy — struggling with himself.”

Venom, starring Tom Hardy, Riz Ahmed, Jenny Slate, and Michelle Williams, opens October 5.