To start the process, look at Stephen Pastis' strip "Pearls Before Swine."
If you've follow "Pearls Before Swine," you know that Pastis has riffed on the squeaky-clean single-panel comic "Family Circus" before. And perhaps you might think it was Pastis just having fun at another strip's expense.
Now look at the Family Circus panel for the same day.
If you saw the "Family Circus" without the "Pearls Before Swine" strip, you might think this was just another Not Me gag.
But it's not.
Usually Not Me runs away with a mischievous glance over its shoulder. Not this time. Note that Not Me walks away with a shrug -- not even it knows who threw the sunflower seeds on the floor.
And there in lies the genius of this collaboration. By breaking the fourth wall (in this case, the barrier between comics), Pastis and Keene have delivered a joke that is far funnier (in part because its unexpected) than either strip delivers individually.
Now that's comic genius.