One of my cats (M. Coon/Himilayen mix) tries to 'dig' through a mirror. After awhile with no success, he will go look behind it. He just can't figure out why he can't get to that 'other' room, or what that other cat is doing there. On the otherhand, my other cat has NO interest, and when Kedi starts his digging, he looks at him like he is crazy. Kedi will also do this with the sliding glass door.