(Strip Number 6724, Original Publication Date, 22 May 1988)
Panel 1: We start things off with John and Elly trying to sleep when a complication is introduced: Farley barking at something.
Panel 2: Elly reacts to this the way she does to any sort of disruption when she's trying to sleep by succumbing to homicidal rage.
Panel 3: The strip most people actually see has Elly panic when the dog barks at whatever.
Panel 4: Having noticed that he's outside and barking at something, Elly wonders who let the fucking dog out this time.
Panel 5: This, of course, transitions to Elly standing outside bellowing for Farley to come inside.
Panel 6: Since his natural reaction is to flee because he remembers that loud noises coming from the angry creature who is just always angry mean pain, Elly continues to holler for him to come in NOW!!!!!!
Panel 7: Elly's hostile screeching finally wakes up a baffled John.
Panel 8: When John asks Elly what's going on, she explains that she let the dog in.
Panel 9: He sets up the stupid punchline by asking her why.
Panel 10: She baffles him when she asks if he wants the dog to wake the neighbours.
Summary: The 'joke' is that Elly doesn't understand that her yelling is just as loud as the dog's barking. This dovetails nicely with a long-term pattern in which she's totally unaware that she's seen as someone who just stands around bellowing in rage all the time.