(Strip Number 572, Original Publication Date, 15 March 1984)
Panel 1: It would seem that John found out about the current situation the same way Greg will find out about Sera the dog. This is because he's genuinely shocked that they now have a hamster named Humphrey. Given that Elly is just now telling him that it's only for a week, it would seem that they're communicating as well as ever.
Panel 2: Before John can start talking to Elly about the importance of telling him things like this, he's alarmed by the fact that Mike asks Elly what would happen if they gave Humphrey to the dog.
Panel 3: As an angry John takes the hamster away from a protesting Mike before he gets any more bright ideas, Elly simpers that it's supposed to teach him responsibility.
Summary: Well, watching Farley maul Humphrey to death would teach him something. Said something would be that life ain't no damned cartoon.