Where does it go during the day? I know the kid saw it, but why didn't he see anything in the morning? Or the maid, for that matter. Is it a spiritual thing that uses the sheets to show itself? And if so, how exactly would it have hurt him? Suffocation perhaps.

Yeah, he is not so observational. But I think that he is the type of person like myself who likes to come up with logical things to explain illogical things.