After Heddy receives the phone call from her father, she hangs up and takes the phone off the hook. As she walks away, a busy signal is heard. Heddy yanks the phone out of the wall, yet a busy signal can still be heard.
When Allison follows Hedy to the sex and bondage place, there is an older man with long hair and a woman coming down the stairs after her. However, when Hedy passes another man and woman standing at the bottom of the stairs, the man and woman who were following her are now in front of her having an argument.
When Hedy kills Sam with her shoe, it's still in his eye when he falls down near the door. When Hedy stands over him, poking him with her toes, the shoe is back in her hand.
Hedy holds the knife to the centre of Allie's throat; when the knife is removed, the cut is on the right side of her throat.
After Hedra kills Graham (or rather, thinks she has killed him), she comes back to Allison's apartment, and takes a shower. After the shower, she wraps herself into a large bath towel and goes into her bedroom, where Allison follows her. But, suddenly, about one second after she has entered her room, we discover Hedra wearing a night shirt and a sweater. Apparently Hedra is a better quick-change artist than the world-famous Arturo Brachetti.
On Allison's pay record on the computer, the pay dates are stated as 1st and 15th August 1991. Mitch states that the 15th pay is overdue and it is a Friday. Both of those days actually fell on a Thursday.
As Allison falls to her knees to vomit in the bathroom, the toilet rocks noticeably as she grabs it, showing that it is a prop rather than a correctly installed fixture.
When Allie and Sam embrace in the apartment, after Heddy leaves, Sam can be heard telling Allie he loves her and wants another chance as they embrace-but his lips aren't moving.
A crew member's shoes can be seen in the mirrored ridge around the table in Mitch's office.
When Heddy comes back to the apartment and throws an item on the table that's near the wall grate, she inadvertently knocks a ceramic bowl to the hardwood floor which makes a loud crashing sound while loudly calling Allie's name. She then kneels down on the floor because she hears Allie and Graham talking about her through the grate - yet Allie and Graham didn't hear the crash OR her name being shouted through the grate in his apartment.
When Allie and Hedy enter the hair salon, the boom mic is reflected in the top right corner of the right-hand glass door.