Lol, cats are very peculiar but they are a lot more attentive to things we don't notice. If your house is raised heshe may smell an animal under it. If the house it not raised shehe may smell something in the hall. And his way of letting you know something is there is to back away slowly so you take notice. But then again there is a million things it could possibly be. My cat loves to walk in my room in the morning meow once to let me know he is there and then he walks off. I'm like your silly cause I'm not chasing you hehe.
Possibility is there is a smell that it doesn't like or reminds it of a time something negative happened to it.
Time to decorate, cats are fussy!
Just checking on his territory.
Just wants to know he can
Believe me there is no understanding cats. Don't even try it will only make you crazy.