EXCLUSIVE: How 'The Flash' Director Kevin Smith Brought Killer Frost's 'Iconic' Cold Kiss from Script to Scree

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"That was cold, Flash, but this is colder."

And with those seven little words, tonight's all-new episode of The Flash delivered one of the most iconic villain attacks in DC comics history!

Caitlin Storm's (Danielle Panabaker) journey has been a bit of a slow burn so far in season three, (pun totally intended!) but this week's hour was fully devoted to discovering more about her evolution into the cold-hearted villain Killer Frost.

And there was one moment in particular from tonight's episode that director Kevin Smith full-on fanboyed over: "She gives [Barry] the f**king cold kiss!" he gushed to ET ahead of tonight's episode.

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"That they have done a zillion times, probably, in the comics with Killer Frost and it's one of the first time I think it gets done [on screen]," Smith said. "I was so happy that it was in my episode!"

"For one brief moment, not only were we making an old issue of Flash, but we had this real Batman Returns kind of positioning where she's kind of straddling on top of him like Catwoman was when she was kissing Batman on the roof with the mistletoe," the 46-year-old director continued, "So we're homage-ing s**t left and right while doing one of the most classic Killer Frost moves in the comics: the cold kiss."

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Smith admitted that he had one goal in mind when filming such a "thrilling" on-screen moment: "I didn’t want to f**k it up," he said bluntly. "It's tough to do a surprise kiss on somebody, particularly when Barry is a little bit taller than Caitlin and the positions of where they were initially in the scene didn’t really lend itself for the most fluid of motions."

In addition to vertical challenges, Smith revealed that they were also battling the temperamental Vancouver elements when filming the lip-locked scene. "We were doing it in pouring rain one night in some of the most miserable conditions, but these kids, man, you wouldn’t know it," he said. "They just 100 percent on every take."

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Smith marveled at what an acting "pro" Panabaker was during each and every one of her scenes. "She processes any comment you've got very quickly and knows what you're talking about," he recalled. "And most of the time, you don’t even have to direct her, she knows exactly what she's doing."

Despite minor setbacks on set, Smith confessed that he could not be more proud of the episode he directed and how he was able to bring the iconic cold kiss from script to screen.

"For what it is, in terms of how it's not a passionate, romantic kiss, I was very happy with how it all came together and I give full credit to the kids because they made it work. They made something that people wouldn’t do normally in the real world seem plausible," Smith said.

The Flash airs Tuesdays at 8 p.m. ET/PT on The CW.