And I'm wrong; the unifying theme for the week is Elly's crazy life.
Panel 1: We start off with her kneeling down to tell a dejected Michael that there some words he simply cannot say.
Panel 2: She points her finger at him and she that she knows that he sometimes hears adults using bad words sometimes but that's no reason for him to do the same.
Panel 3: He says that that's not FAIR!! To him, they're just words; grown-ups know what they MEAN!
Summary: Elly's bafflement at this answer is mildly forgivable; she does know that Mike doesn't know what the curse word refers to but she also knows that having him race around swearing would get him into trouble. It seems to her that her attempt to reason with him kinda failed. Too bad that John will come in with his solution: curse in my presence and I'll tan your @#$%^$@%#%@# hide.