After forehead recontouring, there is often a connection between the frontal sinus and the space under the forehead skin. When you blow your nose, air can be pushed into this space. If you push against the skin with your fingers, you will hear a characteristic crackling sound. This is completely harmless. This air escape will disappear over time as the skin reattaches to the bone. Be careful not to blow your nose too hard, and to apply pressure to the forehead with your hands when sneezing, coughing, etc. This will help reduce the amount of air pushed through this area, allowing it to heal faster.