When Dean first walks up to the dead tree in the cemetery, his Ball Chain necklace jumps in and out of view. As he backs away and the camera pans below Jensen, you can catch a glimpse of the Ball Chain necklace under his shirt. After the aerial shot, it comes to the front of his shirt. Then jumps back under when he starts talking to Sam.
(at around 29 mins) Sam and Dean talk in the car about ways to kill a zombie before a long shot of the Impala driving down a dark road. The person sitting in Sam's spot holding the flashlight is obviously not Jared Padalecki.
After Angela crashes her car, the closeup on her blood soaked phone shows that she is on a TELUS network. TELUS is a Canadian mobile phone network available in British Columbia where the show is shot. It is not available in Illinois or anywhere in the United States.
In the first cemetery scene and the end of the episode, interior of the Impala is black instead of tan.
The most commonly mentioned way to kill a zombie is decapitation.