In the final fight scene between Michael and Gabriel, Michael is knocked onto the glass counter top with his gun just within reach. As he grabs the gun Gabriel drop his spike anvil smashing the glass but in the next shot when Michael stands back up and the counter glass is intact.
When Audrey is in the minivan, one of the possessed scratch the window leaving visible marks, in the next shot the scratches are gone.
Early in the film, when the two police partners are driving down the street, the Latino officer is sitting in the passenger seat, and the white officer is driver. But when they stop to confront Paul Bettany, the Latino officer exits the patrol car from the driver's side, and the white officer from the passenger side.
When the old grandma toward the beginning of the movie bites Howard's neck, Kyle rushes over to help and starts to take off his scarf to apply pressure to the neck. When the next scene pops up, the scarf has turned into a napkin. The next scene shows it again as a scarf.
When you first see the truck carrying the pipes which the view is from the back of the truck looking forward you can see two stacks of pipes on the back of the truck. But when you see a shot of the truck later there is only one stack of pipes.
At the end, when Gabriel flies onto and then inside the fleeing police car of Jeep and Charlie to get to the baby, Jeep accelerates to 100+ and then slams on the brakes, which propels Gabriel out the rear and onto the road. That is impossible. In reality, if you slam on the brakes of a moving vehicle, anyone and anything not secured in the vehicle is propelled forward with equivalent force and speed.
In the opening shoot-out when Michael shoots Burton the slide is locked back on the Glock pistol in his right hand. As he immediately turns and walks to his left the slide of that pistol is forward.
When Charlie's baby is being born, you can see there is no umbilical cord.
EDIT: There are two simple explanations for the missing umbilical cord:
First, there is a medical term for babies born without an umbilical cord, it's called omphalocele - a birth defect of the abdominal (belly) wall.
Second, since the child was never supposed to exist, this could be intentional because the child is an abomination..
Shots of the parking lot of the diner lack some vehicles for all the occupants in the diner. Some are accounted for but some are not.
EDIT: All people and cars are accounted for, *grandma red car, *Bob, Charlie, Jeep, Percy live there, *Howard, Audrey, Sandra black BMW inside the garage, *Kyle black SUV.
The gas pumps outside the diner are shown in various early shots with having no hoses and presumed nonworking. Late in the movie, when a family drives up in a van to a pump, the father gets out and pumps gas.
EDIT: A shadow from the left pump's hose can be seen on the ground between the two pumps in the earlier shots.
Jeep is outside alone, and observes the enormous fly storm approaching, plus huge, rolling, ground-level clouds coming from another direction. But the next time he is seen, he's studying the BMW in the garage, and doesn't seem to be aware of anything weird going on at all.
EDIT: He was told to have the BMW fixed and the owners on the road before nightfall. Jeep is following the orders that Bob, his father, gave him.
When Michael shoots Burton, the cop seen early in the film, a crash mat can be seen on the driver's side of the patrol car as Burton falls to the ground.
In the final fight scene between Michael and Gabriel, Michael in knocked onto the glass counter top with his gun just within reach. As he grabs the gun Gabriel drop his spike anvil smashing the glass but in the next shot when Michael stands back up and the counter glass is intact.
When Michael takes the shotgun away from Bobs forehead, it should have left a circular mark. No mark is visible.
When the ice cream man is approaching, the camera alternates between the characters watching the truck and the truck coming closer. After a shot of Jeep and Charlie looking out the window, the ice cream truck is shown from the front. While the truck is facing the camera, the silhouette of the ice cream man can be seen in the passenger seat turning a steering wheel, facing to the right, instead of in the driver's seat facing forward.