When Tommy defaces the portrait of Harry, the spray paint becomes suddenly faded in one shot, then later the spray paint is fully back. The paint also has different stages of "running" as well as the shapes of defacement changing several times, showing the need for several takes hours or possibly days apart.
When Dick is sitting on the sofa in the Solomons' living room, the shadow of a person is moving behind him, near the bathroom door.
The aliens have been on earth for over five years, during which time they have gone to school, attended many sporting events including the Super Bowl and yet when the National Anthem is played, they act as though they have never heard it or even heard about it.