How come words appear backward in a mirror?

How come? A flat mirror reflects the light bouncing from whatever we hold up to it—whether a newspaper or our own adorable faces—in straight lines. So the left side of your face appears on the left side of the mirror, the right side on the right. The top of your head is at the top of the mirror. A mirror reflects back what we present to it. When we turn a newspaper headline around to face the mirror, it reflects it back, letter for letter, left to right: backward. If the headline were on a transparent piece of glass, and you turned it around to face the mirror, you’d see that it reads backward through the glass, too. (Try this with the logo on a drinking glass.) (Some say the key to the mirror mystery is that mirrors reverse “in” and “out,” which is why, when you point at a mirror, your reflection points back at you.) If you really want to, you can see your true image—your face in the world—by using two mirrors. Set the mirrors at a right angle, like two walls meeting in the corner. When you look at your face in the corner—your true face—you may be shocked at what you see. Despite photos and home videos, few of us have really seen—up close, in real time—what we look like to others. Everyone’s face is a little off-kilter in some way—one side of the nose a bit different from the other, eyebrows not exactly matched. Looking in a regular mirror for years, we don’t notice these small imbalances. But looking at your true image makes every quirk evident. Moles and freckles are reversed; your smile is slightly crooked. And perhaps the most unsettling thing: Your hair is parted on the other side. If you can stop looking at your new mirror self, hold up a newspaper . . . and read the headlines.

A mirror reflects back what we present to it. When we turn a headline around to face the mirror, it is reflected back, letter for letter, left to right: backward.