It's a new-ruin that shows us where Farley was during the camping trip.
Panel 1: As Elly and Mike head to the Puppy Palace Kennel to pick up Farley, she notices that he looks sort of worried. Her response is to ask "We're just going to get the dog, Michael; why are you so worried?" Mike says "Well.....:"
Panel 2: As the mutant woman opens the door to Farley's cage, Mike says "....we never took him on the camping trip an"
Panel 3: His train of thought is derailed as a happy Farley bounds up to him and knocks the wind out of him; he goes OOOOOFFFF in response.
Panel 4: Farley Lick-lick-slurp-licks his beloved owner's face in delight.
Panel 5: As Farley prepares to show how happy he is to see Elly, Mike remembers that he thought that Farley would be mad at them for leaving him behind.
Summary: This is a rare example of Lynn not only taking the time to show us something happening but also making that thing serve the purposes of the story. Too bad we can't get used to it.
ETA: Lynn recycled one of the throw-away panels from Sunday's strip into a new banner.