Eddie Redmayne takes the idea of suffering for one's art seriously.

For his Oscar-winning role as physicist Stephen Hawking in The Theory Of Everything (2014), so committed was he to staying in character that he almost permanently damaged his spine from sitting slumped over in the chair for long periods of time, the way Hawking, a wheelchair user, does.

He is at it again in Fantastic Beasts And Where To Find Them, the new Harry Potter spin-off movie in which he plays the wizard, Newt Scamander, an expert on magical creatures who has to retrieve some of these beasts when they escape and wreak havoc in New York.

The 34-year-old British actor sheepishly reveals he pulled a groin muscle while simulating a mating dance with one of those creatures, which were brought to life with a combination of computer-generated imagery, puppets and animatronics.

In a one-on-one chat with The Straits Times in New York, Redmayne downplays each of these injuries.

With The Theory Of Everything, he admits that his spine began to change shape during filming and that "it was bad", but says in the end, "it was fine - I had a good osteopath". And when he hurt his groin during his overly enthusiastic seduction of a female Erumpent - an enchanted rhinoceros-like creature - the damage was mostly to his pride.

"J.K. Rowling usually writes these long descriptions in her script, but here all she said was, '...and then, Newt performs a mating dance'. And I thought, 'This is a nightmare. What do I do?'"

That is when Redmayne called Mr Alex Reynolds, the movement coach he worked with on The Theory Of Everything and his Oscar- nominated turn on The Danish Girl (2015), in which he played one of the first people in history to undergo gender-reassignment surgery.

"We just went down this YouTube rabbit hole of looking up the mating rituals of birds and things.

"I wish there was a way other than me in the rehearsal room being filmed by Alex making a complete fool of myself and sending those to director David Yates.

"There are some really humiliating videos of me out there and what ends up in the film is quite humiliating," says the actor, whose back was covered in bruises after rolling on the ground in that scene.

Mr Reynolds was drafted into other aspects of Redmayne's zealous preparations for this movie, which saw him helping launch a "wand school" for him and co-stars such as Colin Farrell and Katherine Waterston, both of whom also play wizards in the film.

The classes were necessary because wand-waving is a lot harder than you might think, he says. "I had this moment when I was given the wand - it's the moment your inner nine-year-old has been waiting for all your life," says Redmayne, who has a five-month- old daughter, Iris, with his wife, publicist Hannah Bagshawe, 34.

"I picked it up and got stage fright and was embarrassed by how inept I was with it. So, Alex came just to help us release our inner kid."

All that wand-waving caused a case of repetitive strain injury for him and the other actors. "I saw Colin Farrell, who had quite an intense day of wand-work the day before and he said, 'I've got wizard's elbow.'

"And it's true because it's like playing tennis without a ball to hit - the wand is little, but you're flying your arm around like a mad person, so injuries are sustained."

His preparation is the product of wanting to get things right - a desire that remains unchanged despite his growing resume and success.

"I don't think that ever goes. And for me, that's quite a good thing because you can channel that anxiety in an interesting way.

"So, I haven't found it getting easier. But I have found the capacity to block off certain thoughts. Like, with this film, about the scale of it or how people loved the Potter films and what's at stake and not wanting to screw it up. I'm getting better at blocking that part of my head because it can stultify you."

Winning the Best Actor Oscar last year does not mean the perfect roles fall in his lap now.

"For me, the things you want are always the things out of your reach. So, you'll get offered parts that people think you're right for, but the parts I feel like I've done better work in are the things that people didn't think I was right for.

"So, maybe you get offered more parts, but the things you really want, you're still having to fight for - and that's the way it should be."