I killed 4 dragons i think And i found 3 of those writing on the wall.. in caves that unlock new shouts.. So i got the sprint shout (you get at graybearded guys) and the other shout you have from the first dragon.. And cuz i found two of those signs on the wall i have 2 " empty spots" But then i killed 3 dragons afterwards and neither one of them was filled-.- Do i need an item or what do i need? or how to capture dragons souls!