That small, handheld Geiger counter that Dave uses, would never be able to detect radiation as far as they drive and walk to track the source.
In one wide shot, the creature wears tennis shoes while returning to the lab.
The corpse breathes during the morgue scene.
When Zaat drinks the medicine in the pharmacy, you can hear the fluid draining from the suit on to the floor.
After the monster trashes the drugstore and walks out to the right side, a shadow on the left side moves around on the floor.
When Walker Stevens is in bed and Rex is talking to him, the shadow of a boom mic is persistently visible before Martha joins him and the monster spies them through the window.