Whisk the egg whites with an electric beater at medium speed until they form stiff peaks. Add the salt and sugar and continue whisking at the highest speed until the mixture is shiny. Put in a piping bag and pipe out the mixture in the shape of ghosts or bones. Bake at the centre of the oven at 125 °C for just over 1 hour. Place on a wire rack. Make eyes for the ghosts with melted chocolate or icing.