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The ghosts are persons who forgot that to say to us something. Some are angry, and haunt castels, forests...
Others speak to us to help us. They love night, and move objects to draw our attention.
I think so they exist.
The monsters was created to frighten the childrens. When they don't want to sleep, the parents tell a history with many monsters. Kids are scared, and sleep.
The mummy exist, but they don't walk on the pyramids, and they don't drink some blood. They stay in them grave, and don't move.
;-) J'éspère t'avoir aidé !