The handwriting on the note passed through the hole in the wall between Everett and Sharyn changes between shots.
Sharyn is reading an online article about Cassandra's case, the heading states "Suspected Arson Hospitalized After Mushroom Poinsoning". A person who starts a fire is an "arsonist", but the act of something burning is "arson".
In the beginning as Sharyn is anaesthetized and the doctors prepare for surgery, her eyes are open.
When Everett's tongue is cut off for the second time, the cutting tool is shown placed along the centre of his tongue and facing downward, as opposed to across. This would split, not sever, the tongue.
Sharyn slashes her boyfriend's throat while she is lying on the carpet and resting on one hand, and he standing upright. She could never have made that distance for contact.
While Cassandra's character has no hair the actual bald cap being used by the actor is obvious from the outset. It can be seen around the ears, over the forehead especially, when the actor frowns, and weirdly she has to always wear a scarf round her neck to hide the creases at the base of her head/back of neck.