A metallic cavity does not have charge on its inner surface, resulting in zero voltage inside when referenced to the cavity itself. However, if the cavity is at a high voltage relative to an external point, it can potentially shock someone who completes a circuit to an outside conductor. Current, not voltage, is what causes electrocution, and the human body’s skin provides significant resistance, especially when dry. While high voltage demonstration equipment typically stays below 1 mA, experimental setups can exceed this, posing risks. Understanding these principles is crucial for safety around electrical equipment.