In the episode "The Springfield Connection" (where Marge Becomes a Cop) there's a scene of Marge picking out some canned ham in the Grocery store. When she decides she doesn't want the regular ham, she puts it back where she found it and picks out the Deviled Ham. It cuts away for a second, then it goes back to the shot of Marge and the canned ham. And if you notice, the Can of regular Ham that Marge put back Mysteriously has Disappeared.