When Mather gets into a shootout with Sam and Dean at the bank he fires at least 10 shots without reloading, even though he is carrying a six-shot revolver.
After telling the team about Dave Mather, Dean says "I'll get my boots on!" He has been pacing the entire time, with sound effects of boots on wood flooring.
The episode is set in Kansas, yet the distinct large, jagged Rocky Mountains can be seen in the background. Kansas is too far from the Rockies, and as part of the plains, would have no similar geography. Any hills or mountains in Kansas would be rounded and rolling.
There was no reason for the bank guard to die, as a Seraph Castiel has the power to both heal people and bring them back from the dead. He has brought several people back from the dead in the past, including Bobby.