 Complete the following phrase:  A shield is a form of magic which allows the user to stay invisible to most observers. Fairies shield by increasing their heart rate, causing their bodies to vibrate so quickly that they are never in one place long enough to be seen by the naked eye. Usually, when using the shield, the fairy encounters resistance from non-vibrating clothing, equipment, etc., which causes a slight shimmer in the air. A shielded fairy would cause any object they were sitting upon to shatter under the high vibrations. Fairies have difficulty shielding in areas with high levels of radiation, like 