When Caine first confronts Boner in the bar he points his gun at Boner's crotch. In subsequent edits, the gun changes to a different one.
Diana's lipstick shade is completely different at the end of the scene in the autopsy room than at the beginning.
After Caine shoots inspector Switzer he can be seen holding a Beretta 92F instead of his service gun, a Heckler & Koch P9S.
When the White Boy infiltrates the police station he flame cuts through an iron bar grid which is embedded in the walls. When he's done the grid falls off in one piece, undamaged, with no bars left in the wall.
When the bad alien kills his first victim using the heroin and head extraction, he rips the power line out of the load box. The power goes out in the building except for the neon "Open" sign which stays lit. There is no reason for the neon sign to have a separate power line from the rest of the building.
Crew members and boom mike reflected in the autopsy room light while the cops are talking to the coroner.
Smith's stuntman is visible the first time he's hit by Talec's disc and is sent flying through the air.
Brian Benben carries a 38 revolver but by this time the FBI had already been thru the Miami-Dade Shootout and had transitioned over to 9mm automatics.