When Lisa is talking to the other kids under the pier, her sunglasses disappear between shots (right after she says "like, you know, whatever").
When Marge and Lisa are talking in the bedroom at the beach house, there is a picture over each of the beds of Ned and Maude. In a subsequent shot, one of the pictures changes to a portrait of Rod and Todd.
When Marge is washing the dishes, her pearl necklace changes from white to red.
The number of boys in Lisa's group of new friends repeatedly switches between three and two. When she first meets them under the pier, there are three. In the next scene, when they go skateboarding, there are two. When they are walking on the beach, there are three. Then, when Lisa explains hermit crabs, there are two. In all remaining scenes, there are three.
When Lisa and her new friends are walking along the beach there are three boys. When they stop to look at the hermit crab one of the boys is missing.