Then after the charge is equalized and you touch the object directly there is no electricity to flow and no pain. The spark struck the key or spoon surface and the charge was equalized. The same amount of electricity is flowing when you hold the key or spoon but the flow is spread over the surface of your hand and is below your feeling of pain. You can learn more about static electricity and properties of materials in physics courses and general physics books. Kay, a microwave oven works by heating the food itself and not the air around the food as with a kitchen convection oven.
Heat is the motion of molecules in substances.
Normally heat is transferred between objects by convection or the direct contact of the molecules. The microwave oven generates large amounts of microwave electromagnetic radiation inside the oven cavity. That microwave radiation would go out into space like a microwave radar system, except the oven cavity is designed to keep the radiation inside. Microwave energy more than few microwatt is harmful to living beings. So it is important to keep a microwave oven in good working order and never stay close to it while it is operating.