The family goes to buy a real Christmas tree from a Christmas tree farm but they carry in an obviously artificial tree to decorate.
When Stephen walks Gretchen to her car for some reason the window is wound right down as she gets in it.
When the lead female's SUV won't start due to a low battery, the lead male's sister diagnoses it as a bad alternator. Alternators generate electricity for vehicle engines, and they can only be tested by operating them to see if they output the correct voltage. Since the SUV would not start, such a test would not be possible. The correct process would be to jump start the SUV and then test the alternator.