Just spent several minutes watching Noah interact with the full length mirror on my wardrobe, never seen him so confuzzled!
To say he hates cat noises on YouTube, he didn't appear to be at all bothered by the 'other cat' just in the 'other mylar ball'. Noah pawed at the mirror, popped his head around the side into the wardrobe (left hand door open) and went all the way around the right to see if he could gain access that way. Even after he had batted the mylar ball away he returned to try to get into the other room!
At present he is rummaging around trying to locate Narnia.
Have any of your furballs shown interest in the 'other world'?