Whether you find the titular characters in Tom Hooper’s live action adaptation of “Cats” adorable or horrifying, the truth is that a lot of work went into the singing and dancing creatures. The director and his team pioneered a new “digital fur technology” that merged footage of the actors on the film’s set with VFX, instead of the usual motion capture method that’s been employed in movies like “Planet of the Apes,” and “Avatar.” Here the actors become the cats without losing any trace of their on-set performance.

Hooper’s cats have long twitching tails and ears that react emotionally. The technology, despite helping to create an uncanny valley of cat-humans, is impressively detailed, particularly when you realize that the actors were dressed in tight, green suits during filming. To allow VFX to take over during post-production, the cast wore motion capture suits and face dots, which offered several challenges on the hot set, which was kept heated to help the dancers’ muscles stay loose.

“I found it a bit uncomfortable,” Rebel Wilson, who plays Jennyanydots, told Variety of the costumes. “It was a couple layers and we had a lot of battery packs and a lot of wires down our legs and backs. Plus, you had two mics. The sound is 100 percent just the live sound [so] we had double mics to record everything in case one mic failed. And then we had the inner earpiece so we could hear the accompaniment. So you’d have all those packs on your back as well and they would get hot. It was quite challenging.”

And if you needed to use the bathroom during filming, that was another process in itself, which involved taking off the suit and recalibrating everything. “It was a big decision as to whether you wanted to go to the toilet or not,” Wilson added.

During filming the cast members had to constantly remember to move like cats, which they learned in “cat school” ahead of filming. Much of the challenge was being present as a cat rather than a human and figuring out how each character might walk and jump and pounce.

“It’s an absolutely unnatural thing to do for your body,” Robbie Fairchild, who plays Munkustrap, said. “We had a physical therapist on set all the time. There was a day when I had to jump up, unassisted, on to the top of a gravestone and by the end of the day, because we did it so many times, I couldn’t bend my legs anymore… Our bodies just aren’t made to do what cats do, but by God we tried.”

“For me, the hardest thing was probably trying to be a cat whilst singing,” Francesca Hayward explained, who stars as Jellicle newcomer Victoria. “Or just doing quite human things like walking – leaping off things was a little bit easier.” The actors also had to consider their imaginary cat parts, like whiskers and tails, as they moved and danced through the scenes.

“That’s something you have to be aware of while you’re shooting, as well,” said Jason Derulo, who plays Rum Tum Tugger. “You have to remember that your tail is moving and you have ears on top of your head that are also a part of you. And you smell things before you see things as a cat. It’s being aware of those little idiosyncratic things.”

Some of the characters wear clothing over their furry cat bodies (although some don’t, for reasons that aren’t completely clear), so the VFX team devised a way to help the coats fall over the invisible tails. A small cylindrical piece that would attach to an actor’s backside, which, of course, led to the cast dubbing it a “butt dick.”

“It had a velcro circle and the butt dick would just go on,” Wilson said. “It did look like a dick… I would have mine Velcro-ed – not in every take, but on a lot. It also helped remind you you had a tail.”

“There was only one and it would go on adventures,” Fairchild added. “We found it in the parking lot of the studio and we brought it back one day and they were like ‘Oh my God, we had no idea where it went.’”

The final effect of the cat-humans is slightly shocking, as evidenced by the early trailers for the film. The cast members, too, were initially taken aback by how they looked as cats, although there was also a sense of relief in knowing that their efforts on set had paid off.

“It was a discovery for us because while we were filming we didn’t get to see those things,” Jennifer Hudson, who plays Grizabella, said. “We had use our imagination and I think that’s another thing we all tapped into and realized, ‘Oh wow, I have an amazing imagination to embody this without fully seeing what I’m supposed to be.’”

“We had to imagine so much on set what we were going to look like and embody all these things we didn’t have at the time, like tails or ears on the top of our head, so to see it for the first time was pretty cool,” Hayward added.

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