Doors will mysteriously open. You put your hand on the handle, to open it and it suddenly opens on its own. And you walk through and that's it. There obviously… someone's opened the door, but there's no acknowledgement there. “Oh you know, it's ok I've got the door for you”. So, you know, just “Hello” especially if someone's helped you before, just again using your name, because the name, for myself, takes the place of recognising the face.