Almost my entire life, my mother would refer to my obesity as "your weight problem". You could almost hear the quotation marks in her voice. Then I lost 90 pounds and robbed her of a big conversational topic. But that's another story.
The 9 Dogs story is that Meg and Jinx both have weight problems. I don't have a canine BMI chart but Meg has got to qualify as obese, while Jinx is too skinny. Berry's pretty hefty too, but his weight seems to suit his stocky, muscular body while Meg's weight is just...porky. Teddy is smallish but just right. Jinx, the tallest pup, is downright scrawny. Or he was until Mr. P. started feeding him a medicinal meal every night (in addition to the meal Jinx shares with his siblings).
The medicinal meal consists of a handful of kibble with a hard-boiled egg crumbled up on it. I'd have to be mighty hungry to enjoy that combination, but Jinx just loves it. He's put on some weight, his coat is shinier, he's more cheerful, and he knows exactly where the hard-boiled eggs are stored in the fridge. Of course, now that he's accustomed to this treat, it's no longer a treat. He will never, ever let us forget that he has to have his daily egg.