Factual error: Ruthie gets impaled on a jagged shard of glass from a modern shower door, but shower doors are made of safety glass (since 1977) - when they break they don't leave sharp knife-like shards, only tiny pieces.
Continuity mistake: In the beginning, Katherine Heigl is working on a cadaver and has surgical gloves on. When she thinks someone is after her, in the close up of her squeezing the surgical knife, the gloves are gone.