no ghosts, just fallable human brains that have evolved to detect and respond to patterns even if there is nothing actually there. Think of a rustle in the bush, better to think it is a tiger and respond accordingly and be wrong (type 1 error) than it is to think it is nothing and not respond and get eaten by a tiger (type 2 error). Thank evolution and your liimbic system! But have as much fun with scaring yourself as you want. Cheers