It's mean to abuse your grandchildren.
Gary is watching his grandson Tony while his parents are out of town and Tony has been misbehaving.
Gary wants to stop Tony from misbehaving.
Gary tells Tony that he's been writing down everything that Tony does, and he'll tell his parents all about it.
Gary takes Tony and locks him in the empty attic because he can't make trouble up there.
Tony quickly snaps back into a good child when he realizes his parents will find out about this.
Tony is traumatized and scared of being alone in the dark and damp attic all day.