[Politicalmom]

Uh, they were too LAZY to shut the car doors, and how many dogs do YOU know who understand "Get back"?

MY dog understands sit, lay down, stay....NOT "Get back!!".

[Republic of Texas]

They weren't too lazy, but if you shut the door, then you don't get to hear your "subjects" beg some more. Also, it is a tacit admission that the people you have subjugated on the side of the road, might be human. It's also harder to kill the dog if it's still in the car.