Years of reading detective novels pay off for Dottie as she is finally able to solve the mystery of the missing food.
Dottie presents Marmaduke with a plate of cookies and accuses him of having indulged as he has barbecue sauce on his whiskers. Most likely, whatever Marmaduke did eat that contained barbecue sauce, he didn't care for as he didn't lick his chops afterward as most dogs do. Marmaduke appears to be thinking, "God, what a bitch! How the hell does Phil put up with her?"
In something unrelated, Marmaduke appears to be seated on a large, green ball.