The new survival film sees the Killing Eve star play a mother who, alongside her baby, tries to reunite with her family after London is submerged in flooding.
Speaking exclusively to Digital Spy, Comer explained that "speaking to motherhood" was the largest challenge and something she really wanted to "get right" and feel "truthful", especially as she is not a mother herself.
"Especially when you read a script and within the first scene, it’s a labour scene, and it’s not quick, it’s extensive," she noted.
"We wanted to be thorough with that depiction. When I think about the physicality of being pregnant. I myself I’m not a mother, so there are many instincts and knowledge that I didn’t have, so it was about making sure that I kind of dealt with that," Comer continued.
"I really love that, I have to say, when I think about the labour scene, the conversations we would have about breath, and where you feel it in the body. It was attention to detail we really wanted, and we really strived towards, and achieved.
"So there are things like that felt like a challenge, and also the sense of being in every scene with a newborn. The babies are from eight weeks old to eight months. That responsibility of not having been around babies an awful lot, and learning how to hold them, how to take care of them."
The actress also spoke about what attracted her to the role, explaining that the chance to work with director Mahalia Belo proved an exciting prospect for her.
"I was a huge fan of her previous work, so when the script came through with her name attached, I was already immediately excited," she recalled.
"And then I read the script, written by Alice Birch, who is also a genius, and I’m also a huge admirer of. I was really moved by the story and wanted to meet Mahalia as soon as possible and hear from her what it was that she was envisioning."
Belo herself also revealed why she wanted to adapt Megan Hunter's original book The End We Start From, saying: "For me, I read the book quite a long time ago, I think around the time I had my first child. But actually this film specifically probably does trap my parenthood.
"It was so poetic and so beautiful, and really moved me. And later I read Alice Birch’s script just after the lockdown in COVID. And I had a second kid through that experience, and it sang to me in a completely different way. And I just felt like, right now, this idea of what future we’re going to have.
"Also I love that it spoke about that first year of parenthood, which is a moment of absolute change: your body changes, the way you have to think completely changes," she added.
The End We Start From is released in UK cinemas on January 19.
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