ETA: Thanks to
Panel 1: As our story begins, it's another weekend afternoon at the Pattermanse. We see Mike smiling as he bends a water hose.
Panel 2: He looks over the corner.....
Panel 3: ....and lets the hose go.
Panel 4: We next see John get blasted in the face by the sprinkler because he was too dim to check the tap.
Summary: If the joke had been current at the time, someone would probably have told Lynn that Hank Ketcham just phoned and he wanted his punchline back. It's amazing how derivative she used to be, ain't it? Also, we know what Panel 5 would have been given John's temper: "John paddles Mike's behind because he got outwitted."