You won't believe what The Big Bang Theory stars had to wear on set

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Kaley Cuoco has shared a behind the scenes picture from the set of The Big Bang Theory, but it's not exactly what fans might expect.

The actress posted a snap of herself with co-star Johnny Galecki on Instagram... clad in bondage gear.

Johnny Galecki and Kaley Cuoco
Johnny Galecki and Kaley Cuoco (Chris Pizzello /AP/PA Images)

The duo - who play on-screen married couple Penny and Leonard on the long-running comedy series - are certainly a world away from their usual selves.

Top nerd Leonard is more often than not dressed in toasty layers and a jacket, while Penny is pretty much your average well-dressed professional woman (or in yoga pants).

But the new shot shows Johnny in leather straps and with a dog collar, while Kaley almost spills out of an eye-watering corset teamed with fishnet tights. Weird, right?

Along with the snap, Kaley wrote: "#bts of last nights @thebigbangtheory__ #kaleyspolaroids #corsettook15minstogeton @sanctionedjohnnygalecki."

The best bit about the frame? Johnny/Leonard's utterly stunned face.

The pair were shot filming a scene in which they were in a sex dungeon in one of their best pal and roommate Sheldon's (Jim Parsons) nightmares.

Let's hope things return to normal in the wardrobe department for them in the next episode...