Corrected entry: SPOILER ! Heddy cleans the entire apartment to get rid of any evidence she lived there, such as fingerprints. But she didn't seem to care too much about eating and drinking in Sam's apartment right before she killed him.
Corrected entry: When Allie goes to throw up the toilet moves. (01:18:00)
Corrected entry: From the scene where Heddy takes Allie to the fancy salon, and Heddy freaks out Allie by getting her long brown hair cut short and dyed red to match Allie's. Allie gets a trim on her normal short cut, but just as she's finishing, Heddy comes out with her whole transformation - one that would take much longer than Allie's short trim did.
Correction: Not really a mistake since we don't know how busy the salon was, and it's very possible that Allie wasn't taken care of until much after Heddy, as shown.
Correction: I'd say this is more of a character mistake then a movie mistake, as Hedy didn't go to see him with the intention of killing him, only to trick him. She cleans the apartment and dyes her hair black after the murder so anyone with a description of Sam's visitor would describe Allie.