After the Deetzes move into their house, the ghosts of the Maitlands try to scare them away, but no matter how gruesome they make themselves, none of the Deetzes are aware of them except for Lydia, because ghosts are Invisible to Normals.
Example of:
Failed Attempt at Scaring
After the Deetzes move into their house, the ghosts of the Maitlands try to scare them away, but no matter how gruesome they make themselves, none of the Deetzes are aware of them except for Lydia, because ghosts are Invisible to Normals.
