You have often looked into a mirror, of course. But you haven't seen the real picture of your face yet. And why couldn't you see it? When you look into a mirror, you don't see your face as other people see it. You see a reversed picture. If you close your left eye, your picture closes its right eye. If you touch your right ear with your right hand, your picture touches its left ear with its left hand.
　　If you have two small mirrors, you can see your faces as your friends see it. You hold the two mirrors at right angles(角度) to each other and look into them. After some practice you will be able to see the real picture of your face.
　　Now close your left eye and your picture closes its left eye too. Touch your right ear with your right hand and your picture touches its right ear with its right hand! This happens because each mirror reflected(反射) the picture in the other mirror. So you see a reversed picture of a reversed picture, which, of course, is the same as the real picture.