If the heat is too high and/or the ingredients have a lot of marinade (sauce), that could cause the grill top to burn. Stubborn burn can be very difficult to clean afterwards. Wiping the grill top with wet paper towel, or place ice cubes before wiping between cooking different ingredients can help keeping the grill top from burning for easy cleaning. If you burn Yaki Yaki San and it becomes too stubborn to clean, you will need patience. Soak the grill top in hot water for a while, then use a scrub brush (like Japanese "tawashi" brush) to scrub. You might need to repeat the process depending on how bad the burn is.