Static electricity makes these black bits jump like fleas. Rub the plastic cover vigorously with your hand and watch the black bits inside jump up and down. It works best if you rub hard enough to warm the plastic. When you rub the surface of the plastic you transfer negative electric charges from your hand to the plastic. These neagtive charges attract the positive changes in the black bits of formica below. In places where the attraction is strong enough the bits jump up to the plastic.