The varnish streak down the face of the grandfather clock vanishes when Hank wakes up, following his "whack a mole" hallucination.
When Hank passes out from varnishing the grandfather clock, when he falls over he leaves a varnish streak down the clock face. But when he wakes up, this streak is gone.
When Hank is in the garage varnishing the grandfather clock, Peggy tells him she's taking the kids out to buy them "real presents." However, since it's Christmas Day, stores would all be closed.
When Bobby is handing Luanne his present to her, you can see the gift tag says "To Bobby, From DHC". It should have said "To Luanne, From Bobby".
When the computer salesman is typing, his left hand doesn't touch the keyboard.