And I'm almost glad to be wrong; what we have is Elly boasting to John that she's managed to trick Mike.
Panel 1: We start things off in the laundry room; as Elly does her daily three loads of clothes, John asks where Mike is and she tells him that she told him to vacuum the hall stairs.
Panel 2: John watches as Mike rolls marbles down the hose while Lizzie collects them at the bottom.
Panel 3: He then tells Elly what's happening; her reaction is to smile and say "Good!!"
Panel 4: He wonders why that's good because he's not getting anything done.
Panel 5: As she picks up the laundry basket, she tells John "I am!!"
Summary: Well, this is interesting; Elly actually understood how a child's mind works and used that knowledge to her own advantage. What are the odds?