When Charly comes back to his room, disgusted that he had been beaten by a mouse one too many times, he throws his hat onto the dresser where it falls to the floor. Moments later he leaves, and the hat is back on top of the dresser.
When Charley is talking to Mrs. Kinnian outside the building for his night class he is wearing a gold vest. When the camera cuts back to him after Mrs. Kinnian enters her car, he is wearing a blue vest.
When Doctor Nemur, the other doctor, and Mrs. Kinnian are discussing possible complications with Charlie's surgery, there's one shot where Dr. Nemur takes the cigarette out of his mouth, but in the next shot it's back in.
There's one scene where Charly's just woken up from his surgery. The next scene shows him working on a puzzle, and he has a full head of hair and no bandages. If he'd just got brain surgery, he should still be wearing bandages, or at least have his head shaved.