Infection doesn't really occur to Castiel. Just like calling an ambulance had not. They were things he knew about, but did not think about because they had never much mattered to him before now.

The jostle of the bed had Castiel giving Dean a look that, really, was not that distinguishable from his usual looks. But it was there regardless. Ow. Again.

"I know how to fire a weapon." He did. He had done so before, and his aim had been good, despite preferring the simpler methods of his abilities. But that did not mean he understood them the way Dean did or knew their intricacies.

"I do not understand how guns relate to a pressurized spring's release of steam from the earth." But he was picking up one of the guns and inspecting it critically. (This time with his uninjured arm. Good angel. Learn through negative reinforcement)