At 42 minutes, Mrs. Appleyard (Natalie Dormer) is seen clothed, lying on top of her bed. However in the year 1900, she incorrectly has no underarm hair, because in the year 1900, no women shaved their armpits.
At 29 minutes, a black and white photograph of the students and the staff is taken, and then the resulting negative is quickly shown on screen. Mrs. Appleyard (Natalie Dormer) is wearing a dark red dress, and in 1900, all black-and-white film stock is non-panchromatic, and completely unable to capture anything dark-red colored, so her dress should seen as black in the negative, but is incorrectly seen as white in the negative.