Fire the Blue Bird at the left side of the castle. This should cause this portion of the castle to collapse, as well as killing the pig inside. Fire the next Red Bird towards the Helmet Pig. It won't do much, but it'll help clear a pathway for the next bird. The third bird should be launched at the same angle as the second, towards the Corporal Pig. Although this probably won't take out the Corporal Pig, it will collapse the tower above him. Use the fourth bird to clear out any rubble around the Helmet Pig. Throw the fifth bird at the glass above the rightmost pig. The tower should collapse like in step one. Finally, use the sixth bird on the helmet pig again, finishing him once and for all (if the pig from step five survives, use the bird to take him out along with his helmet). The two final unused birds award the player 20,000 extra points.