In the early-on street fight, the white guy spits blood to his side and the blood is black.
After Lucas kills the zombie in the first ten minutes, one hears a siren for several seconds as it has come and gone, then this happens again. No emergency vehicle arrives. It's as if someone turns on and silences a siren twice, and each time turns the sound down or away from the scene.
In the 21st minute the prisoner Lucas smokes' exhales are unrealistic. Either he is not inhaling, or this is poor CGI.