Two things happened at once: First, Aziraphale had come into his line of vision, and an idea was forming in his head. Barnaby only had a cursory knowledge of mechanics, preferring to work through people instead. Even so, he could accomplish a few things just by will. An irrigation sprinkler system surely wasn't too difficult to manipulate.

A crease appeared between his eyebrows for a few seconds, one hand resting on the sprinkler head. Then he opened his eyes, aimed, and shot at the angel.