Revealing mistake: At the end, as Ray's parents walk out the back door, Robert says "extra credit". Look out the door when he says this, and you can see the house in the distance wave as if it were a painting.
Revealing mistake: When Raymond runs out of The Shower at the beginning of the episode, you can see that he's wearing nude colored shorts.
Revealing mistake: When Robert sits Frank and Ray down the top of the set is visible behind them in some shots. (00:19:05)
Revealing mistake: When Debra walks into the kitchen after finding out Ray lost $2,300 she turns the kitchen light on but the light comes on before she touches the switch. (00:11:15)
Revealing mistake: When we see Angela taking Ray and Bernie's order for the first time, look closely and you will see that she's not actually writing on her note pad. She's just moving the pencil up and down. (00:02:45)
Revealing mistake: When Ray runs out of The Shower at the start you can see the boxers he's wearing. (00:00:50)
Answer: War.
By whom?
Edwin Starr.