According to spotts1701, we're about to see that the worse Lizzie acts, the happier it makes Little Mikerobe. That's because Liz has discovered the terriblest, most awfulest word in the world: No.
Panel 1: We start off with Elly exhorting her to finish her strained peas. Lizzie's response is to yell No.
Panel 2: She also yells No and flails about as Elly wipes off her face.
Panel 3: When Elly drags her off to take a bed before being put to bed, she yells No five times in succession and motions that she wanted to stay in her high chair. Mike looks on in confusion.
Panel 4: He tells her that she shouldn't talk like that to Mommy because it's not nice. He rubs in the message by repeating it.
Panel 5: As Lizzie makes drying her off a struggle (owing to Elly holding her in the air and making her fear that she'll fall and hurt herself), he thinks to himself that her behavior does have the minor advantage of making him look good.
Summary: I know that being in the presence of a small child in the terrible twos is a trial; I also know that it's a normal part of their development into independent people. That's where I part company with Lynn; she obviously sees it as an unnatural phenomenon that takes hold of children and makes them defiant for no reason.