When Joon plays poker, she asks for two cards--one can be seen as being a black card. When she shows her hand, she has five hearts.
Joon's bangs change length on her forehead several times throughout the film.
Joon's medical records list her address as Water Street, but later on her Medical Alert Card shows that she lives on Cedar Street.
When the female customer in the auto body shop asks Benny out for dinner, her necklace is tucked into her shirt. In the next shot, the necklace is out of her shirt.
In the park, when Benny goes to help Sam up, his tie is not tied, but hanging loosely. In the next shot it is tied again
We see Sam "playing" a balloon. The balloon is not tied, but then we hear it pop. An untied balloon can't pop. There is no resistance pressure.
In the scene when they are leaving the park, Benny is supposed to thank Sam for his uplifting performance, but before he starts to say thank you, Sam starts saying "no, no, thank you", causing Benny to have to squeeze his comment in while Sam is still talking.
The hospital scene. When Sam gets out of his wheelchair to hug Joon his hat is far more distressed than it was when he & Benny were in the waiting room.