When grandpa comes to talk with Tommy in the city, the window on the car is down a bit, but in the shot where Tommy enters the car, it's fully up.
When Tommy's girlfriend opens the door of the house and checks for him, a shot of house and the pool is shown and it can be seen that the door she is keeping open in previous shot is closed in this one. In the next one she is still shown keeping it open.
When Tommy finds his sister making out with her boyfriend, her hair is completely different from what was seen in the previous scenes and more resembles something seen when she first appeared on screen. Then her hair changes again in the next scene to what was previously seen.
When Tommy is putting his dead mother down on the grave, he puts her closer to the gravestone, but in the next shot she is farther from it.
Daughter comes out of the bathtub wet and puts on a robe, but it's not wet after she puts it on.
Cross turned upside down is shown as a satanic symbol in Tommy's shrine, which is a common mistake horror movies do. Cross turned upside down is actually a symbol used and depicted on paintings in some of the churches and it's a sign of st. Peter who refused to be crucified like Christ, demanding for his cross to be turned upside down because he deemed himself not worthy of being crucified in the position Christ was.
Woman decapitates Tommy with trident off screen in his hallucination. You could hardly do that with a trident, it's made for stabbing, not cutting.
After Nora emerges from her swimming pool, the pentagram "tattoo" on her left buttock is almost completely washed off. Later, when she removes her bath towel, the mark is renewed, but now the pentagram is inverted (when Nora was bending over the trunk of her car in her first scene, the odd point was directed upwards).
When car is set on fire, fire is obviously burning in front of the car and not the car itself.
When woman is branded at the ceremony she acts like it's just a mild pain, while in reality it would be a far lot painful. That's because the pentagram put on her buttock is obviously just paint.
When woman is hurting Tommy with the trident, it obviously isn't hurting him and it's just paint on his neck.
Brian's head is opened up with a shovel. In reality that would take a whole lot of force and precision.
When Nora is buying wine and beer at the store, the cashier says her total is $40. Nora hands her a single bill to which the cashier says her change is $15, which would mean Nora handed her a $55 dollar bill.
A woman goes into the bathroom and gets stabbed from behind, with blood everywhere. Not long after, two women go into the bathroom and see the dead woman propped up on a chair, so they figure she's passed out. No blood anywhere, nor is there blood on her gown.