And how is that fireplace going?

Is this the wall your cat appears to be staring blindly at? Could it be that she expects there to be something different and
still there isn't? Could she be baffled by watching you stare at this same wall for weeks and is merely trying to figure out what was so interesting to you?
Or did she perhaps go to sleep one afternoon and wake up to a different wall and so she is not taking any chances of that happening to her again..keeping her eye on this wall -so that it can't play the same trick on her as the fireplace did?
