Visible crew/equipment: When Mary leans across the drugstore counter to whisper in George's bad ear, there is a small piece of tape on the edge of the counter right in front of her hand, presumably to show the actors where to position themselves for the shot (the tape isn't visible in the other shots showing that same section of the counter). (00:06:55)
Visible crew/equipment: When Sam and his wife get into the car (heading to Florida) George and Mary watch as they drive away, and just as the couple turn around the actor's chalk T-mark is visible on the ground near George's feet. (01:07:10)
Answer: It was a common phrase at the time, like someone saying "oh boy!" or "hot damn."