Character mistake: There's no way that using a regular needle and thread to sew up that wound would work the way it's shown. Anybody who knew what they were doing - which John Cusack is portrayed as knowing - would also know that using unsterilized materials and instruments without a sterile field from an uncleaned massive open wound is a great way to kill your patient.
Suggested correction: The main plot of this film takes place inside the head of a murderer with dissociative identity disorder. The fact that stitching up a wound in that matter wouldn't work is irrelevant to the fact that it is how Malcolm is playing out the scenario in his head.
You're making a good point to invalidate a "character mistake", but couldn't the entry be reclassified as a "factual mistake" and stand as written?
