I don't know about my cats though. The first time Jerry jumped onto our mantelpiece and saw herself in the mirror she hissed at herself and fell off the mantelpiece, which of course had us all in stitches. After that she would just ignore herself in the mirror, but still spend time staring round the reflected room in the mirror.
We thought maybe it was because she realised she couldn't feel the other cat through the glass or something. However, two cats separated by a window still always used to yowl and hiss at each other, or at least notice the other was there and move away.
Can any one explain that, if they didn't know the difference between the real cat on the other side of a window and the unreal cat reflected in a mirror? We thought possibly smell, but they acted too nonchalant with their reflections for that to be the reason.