(Strip Number 806, Original Publication Date, 19 February 1985)
Panel 1: Having come home from the doctor's office, John tells Elly how relieved he is to have the cast off because he can scratch his leg, sleep comfortably and bathe normally.
Panel 2: Having noticed that Elly is smiling at him instead of gushing in sympathy like he expected her to, he asks her why this is because she's never had to endure anything this uncomfortable in her life. (It's at this point that we can see the punchline Lynn is telegraphing.)
Panel 3: He then whines about how she can't possibly know WHAT discomfort feels like because she's never had a cast on her foot for six whole weeks.
Panel 4: When she says "Try being pregnant for nine months", John's brain crashes because he's being asked to do something impossible and understand how someone who isn't him feels.
Summary: Elly would later have to go on and make John wear one of those empathy belly things because he still didn't get how uncomfortable carrying April was because, well, he's simply incapable of understanding the fact that since he doesn't feel her pain, Elly can't be feeling like she's in constant discomfort.