During an interview with CinemaBlend, writer and director Parker Finn talked about how difficult it was to deliver a diversity of disturbing and scary moments throughout "Smile." "All the scares in the film were definitely, you know, bespoke and logistical challenges for every single one of them. I wanted to make sure that we weren't just scaring people the same way over and over again–that there was a sort of escalation to the scares and an unexpected nature to them," Finn explained.
One scene posed a big problem, though: the birthday party scene. Rose shows up at her sister's house for her nephew's birthday after insisting she couldn't come. She brings a present, a toy train the audience saw her wrapping earlier in the film. Except, the train is suspiciously absent from the box and replaced with Rose's dead cat instead.
"The birthday party scene was a major logistical challenge with the extras and so many children around, and also what Sosie had to do in the middle of all of that," Finn continued. The scene is disturbing, both for the characters and the audience. Watching an excited little boy go from celebrating his birthday to being traumatized is mortifying, but it's an integral scene in showcasing how far Rose has fallen.
After the reveal of the cat, Rose sees the smiling entity again, panics, and falls through her sister's glass coffee table in front of the entire party, only adding to the horror these kids witnessed.