Jessica Chastain has found herself at the center of the Other Mommy frenzy, and frankly, that smile is doing plenty of the screaming. Playing both loving mother Ursula and the shape-shifting entity that mimics her, Chastain imagined something supernatural taking possession of her to conjure that wonderfully ghastly grin. Naturally, the result is haunting audiences before the monster even arrives.

Everyone knew Jessica Chastain could act, but watching her manufacture something this deliciously unsettling is another matter entirely.

Speaking on Jimmy Kimmel Live, Jessica Chastain broke down the surprisingly physical process behind the disturbing Other Mommy expression. She imagined the supernatural entity literally gripping onto a person’s skin, creating the kind of strain that builds when holding something heavy for too long. The challenge was then to maintain that tension while still appearing completely harmless to a child.

“So then there's the smile, but really tense, and then, if it's really painful,” she said with the creepy smile while also dropping a tear.

Jessica Chastain then demonstrated how that tension could turn the smile into something far more unsettling, even allowing a single tear to fall while keeping the expression intact. When Jimmy Kimmel wondered where the perfectly timed tear came from, the Academy Award-winning actress simply pointed to her training. It was an impressively effortless display of very deliberate acting.

On Jimmy Kimmel Live, Jessica Chastain also explained that she genuinely focused on feeling the pain throughout her body to make the expression convincing. That physical tension even reached her neck, which viewers can notice in the finished image. Yet amid all that discomfort, the actress still had to make the entity appear gentle, friendly and safe, and all that mixes into her viral creepy smile.

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While Jessica Chastain is dabbling in country mystery on Netflix, she is making Other Mommy even creepier by revealing the twisted story behind her performance.

Jessica Chastain has now dished on the real-life incident that helped inspire Other Mommy, and it is almost too creepy to sound true. During press interviews, Chastain explained that author Josh Malerman got the idea from something that happened to his brother while putting his young daughter to bed. The little girl casually said, “Goodnight, Other Mommy.”

That innocent bedtime goodbye left Malerman’s brother frozen, wondering exactly what his daughter meant by "Other Mommy". The strange encounter became the seed for the supernatural story about an entity that takes the shape of a child’s mother, while also explaining the film’s deliberately unsettling title. And knowing that story makes Chastain’s painstakingly painful creepy smile feel even more disturbing.

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Do you think you would be able to recreate Jessica Chastain's creepy Other Mommy smile? Let us know in the comments!