Mary is wearing one pair of shoes when she leaves the apartment to go to the bank and a different pair when she arrives there.
When Mary goes to meet the bank officer, she is wearing dark underwear (visible through her sheer dress). When she arrives home later, still wearing the dress, the underwear is white.
When Paul Bland leaves to go to the grocery store, he leaves the frying pan on the orange chair by the door; in the next shot, when "the hippie" arrives late, the frying pan is gone.
When Paul and Mary exit the elevator to go their apartment, the doors and carpet colors don't match those seen outside their own apartment in another shot just moments later.
The black plastic bags, which the dead bodies are stored in, are comically too small and easy to carry.
The man killed while Mary is wearing the "cartoon mouse" costume can be seen breathing while lying on the floor.
(at around 1h 15 mins) When Paul throws the bug zapper, it hits the camera, causing the camera to shake up and down and go out of focus.
(at around 1h 18 mins) When Mary, Paul, and Raoul walk into the kitchen, a crew member can be seen reflected in the mirrored artwork on the wall on the right side of the screen.
When Mary is in Mr. Leech's office at the bank, the shadow of the boom mic is visible on the wall.
(at around 1h 3 mins) When Paul asks Doris for help, Paul says, "Yes, but not the kype you're used to." instead of "Yes, but not the type you're used to."