A rat named Steve.

We live out in the boonies and have empty barns at the moment. A rat. Yep a real one has decided that he likes us. Now, we have four. Yep count them FOUR inside cats. Large Maine coon cats. Cats the size of medium size dogs. And this rat,(Whom I've named Steve) just walks right past them on our lower outside mud room landing. The cats just look at him as if he is a long lost friend. They don't pounce, hiss, jump or act like they are going to devour him in any way. He just takes his time and walks on by. The first time he popped out I swear the entire house heard me scream and run back into the house slamming the kitchen door behind me. The cat looked at Steve, he at the cat as if to say..."What the heck is with her? why is she making all that noise?" What could he possibly have to blackmail my four cats with? that's what I want to know? why else would he still be around and not have become 'Steve tar tar' by now.