Goofs

The driver's side windshield is damaged as the main characters are driving down the freeway, leading into the scene where the police are on the P.A. saying, "Remain in your vehicles." Later when they find Nick in the water spillway, the windshield is not broken.

When Madison and Calvin are standing on the door sill of the pickup truck surveying the traffic jam the rear sliding window of the truck changes from nearly closed to fully open.

When Nick meets Calvin at the diner he had been out of the hospital for a day or so and he said it had been over 48 hours since his last dose of heroin, yet Nick only seems mildly uncomfortable. If Nick is using heroin on a regular basis, then his brain chemistry has become dependent on the heroin, so going 48 hours without a "fix" would cause Nick to be in full blown opioid withdrawal. Other then possibly IV administered oxycodone, IV heroin is the hardest opioid to detox from and has the worst and most severe withdrawal symptoms. So by the time Nick meets Calvin in the diner he would be incredibly sick and in a huge amount of agony.

The zombified Gloria and her victim seemingly disappeared into thin air. When Nick is running outside, he looks back and Gloria doesn't appear to be following him so presumably she was still inside the drug den but when Travis went to check it out, she and the other body were both gone.