The nurse is supposedly alone in the subway station, but during one shot (from inside the subway train as it pulls away) we can see several people walking about on the platform; they all disappear in the next shot.
When the prostitute gets scalped, fresh blood runs down her face. However when Frank pulls off the scalp, the blood appears splotched or dried up.
During the scene Frank has tied Rita to the bed, her gag is around her neck during her face shots, but missing in the body shots where he runs the knife along her body.
As Frank is choking the prostitute, her hair noticeably changes between shots.
The candles around the portrait of Frank's mother are lit; but when Frank returns home after murdering a prostitute, the candles are not lit.
Anna injures Frank with a shovel, which cuts through his skin and clothes in the process. Shovels are rather blunt, not sharp, and would in turn be extremely hard to slice through skin and clothing with its broad, dull blade.
When Frank slits the woman's throat on the beach, the knife makes no contact with the throat, even though blood spurts forth from the wound.
When Frank looks at the unconscious prostitute on the bed, freeze frame stills are used to not show the woman moving.
Fake fog obvious when Frank appears in front of the car, there was no fog before that shot.
Obvious fake head used for Frank's decapitation.
When Frank is chasing Anna in the cemetery, there are gravestones present which are very clearly cardboard cut-outs.
When the prostitute is describing her services to Frank, she says "For 75, I'll take you around the world." But her mouth don't match what she's saying.
When the nurse is hiding in the bathroom and is heavily breathing, the visuals don't match up with the audio.
The nurse cries "Open up!" even though her mouth never moves.
The camera's shadow can be seen several times on some of the mannequins in the final scene.
Vaguely reflected from the inside of the subway windows, when the nurse struggles to get into the subway to escape from Zito.