"Expecto Patronum!" he shouted, and a burst of silvery light shot out before materialising into a stag. However, unlike most Patronus Charms, this one did not immediately charge towards the dementors. Instead, it whirled back around towards Harry and the stag morphed into a cloud that encased the Serpent Slayer. The sword blade glowed like a white-hot knife for the briefest of moments, then settled down into a dull silvery light.