At the beginning of the dinnertime confrontation, Helen's position changes. She is kneeling by Annie and begins to stand, but in the next cut, she is kneeling again.
The way Annie holds the doll changes after Helen gets back in bed after learning 'milk'.
At breakfast when Annie is wrestling with Helen, a candle cover is knocked down from a table against the wall. Seconds later, when Annie somersaults out of Helen's grip, it is back upright in its original position. As Annie pulls Helen back to get her spoon, the cover is on the floor again.
Anne Bancroft plays Annie Sullivan with a slight Irish accent. The real Sullivan was born in Feeding Hills, Massachusetts and, despite having Irish parents, had no such accent.
Annie Sullivan has to look up the word discipline in a dictionary later in the film even though she's used it in a letter near the beginning; however, she remarks that she must know how to spell it before teaching it to Helen, and may have simply used her best guess in the letter since nothing was at stake.
Annie's last name is Sullivan. When Annie and Helen are first in Annie's room together and Helen receives the doll, Annie refers to herself as "Miss O'Sullivan."
The sounds Helen is making after having water splashed in her face do not match her lip movements.
Helen went blind at 19 months of age. Therefore, when she finds the hand-held mirror among Annie's things, she wouldn't have known what it was or what it was for; she wouldn't have pretended to check out her own reflection.