When he was 3-4-5 my nephew had *something* that no one could see. He called 'it' "nanna". It seemingly always frightened him. In the middle of the day he would come tearing into the house, cry 'nanna!' and hide himself behind his mother or a piece of furniture. He would sometimes do the same, coming in from a different room.

When he was 20 or so, I once asked him who or what nanna was. He didn't remember.