When June goes up and talks to Beaver, his arms keep changing from resting on his abdomen to being behind his head.
Mary writes two lines on a piece of paper and passes it to Beaver, but when Beaver opens it up, it has three lines plus Beaver's name at the top. Then Beaver writes a note to Mary using small strokes with his pencil, but when Mary opens it up, the message has two words with big underlined capital letters and an exclamation point-something Beaver's hand movements wouldn't have produced.
When Beaver shakes the hand of his girlfriend, the rings on her fingers are missing.
When Beaver and Mary are playing Monopoly, he tells her she has all the office buildings, so she wins, but there are no office buildings in Monopoly, only houses and hotels.
When playing Monopoly, Mary moves her piece and counts off eight spaces, the last move of the game. The dice show a throw of eight. Just a short time later, as Beaver and Mary shake hands, agreeing to only walk home from school with each other, the dice show a throw of seven.
When Richard and Gilbert tell Beaver they've been waiting in the playground for him (after he gets mad at Mary) Richard's shirt has the buttons on the left side. Boys' shirt styles have the buttons on the right side.
After Mary passes a note to Beaver saying he can walk her home after school if he wants, Beaver replies with "Drop Dead" in huge dark letters, but when he's writing the note, you can see he didn't write it like that at all.