Goober mentions in this episode that Deputy Warren is Floyd's nephew. Floyd goes on to explain that Warren is his sister's son.
A camera-pan after Goober and Warren drive off from Andy's house shows a large empty space at the end of his street. In seasons 1, 2, and 3 there had been a dilapidated old industrial building blocking this area. It had originally been built on the lot many years earlier for the 1957 movie, "Reform School Girl."
The shots of Andy trying to close the trunk on the picnic supplies show a modest house in the background. It was a standing facade on the back lot that rarely showed up in scenes. However, in the second season it was transformed into Frank Myer's house for the episode "Mayberry Goes Bankrupt."
Floyd states that Warren is "the image of my sister," which explains why Warren's last name is Ferguson and not Lawson.
When Warren and Goober are at Andy's front door to warn him about the picnic he throws them out. Goober is jostled around pretty violently yet his chocolate milkshake remains completely motionless in the glass. Obviously it's just a prop for this particular scene.