While Kelly is drinking and talking to the cows about going to the dance, the number of beer bottles sitting on the wooden block fluctuates between shots.
When Kelley, Steve and Charlie are sitting in the diner, the menus behind them change direction between shots.
Kelley wears identical blue Oxford shirts throughout the entire movie, which spans one summer. Odd, but possible.
When Kelley is getting out of the shower, you can see his shorts under the top of the towel