While Mr. Lundy is encouraging Sheldon to go on stage, Sheldon's red wig keeps switching between Mr Lundy's left and right hand.
Sheldon trapped Principal Petersen in his office by jamming a chair under the door knob so that the door wouldn't be able to swing open. An office door (or any room door for that matter) never swings outward. They all swing *into* the room to prevent this from ever happening (either deliberately or accidentally).
The PA system that Sheldon defiantly uses in the school office is actually a citizen's band radio. While most CB radios do have a PA function, it is doubtful it would be used in such a setting since it is not adequately powered for such a large building.
Meemaw states that her purse is full of scratchers (scratch-off lottery tickets). The show is set in 1989 in Texas. Neither Texas nor Louisiana (where Meemaw often went to gamble) got state lotteries until 1991.