Have you ever wondered why your microwave oven has all those black dots on the window? Or how about why pen caps have a hole in the top? We spoke to lifestyle expert Trey Boge to learn what all the little details we see on everyday items around the house are designed for. Pen caps have a hole in the top so that in the case that someone accidentally swallowed it, air could still pass through. Those dots on your microwave are actually a screen keeping radiation from escaping.