Screaming Skull Catapults may be upgraded to allow them to hurl the skulls of the race they are fighting. So, a catapult with this upgrade can hurl Orc skulls at Orc enemies, or Dwarfish skulls at Dwarfs. This is even more terrifying than the catapult's usual ammunition, and any unit that must make a Panic test from the Screaming Skull Catapult suffer a -1 to their Leadership.