In the first place, Hartigan isn't entirely sure about the cause behind Lady and Sarah's controversial feud.
There's not many of a time that he's there when they cause an uproar. He only ever heard of the worst instances from those who were present at the scene. That's why he's not certain just how bad their relationship is. He even doubts that they truly hate each other at all.
Seeing how they are interacting with each other right now, though, it seems to him that they can be on the same page after all.
"H-Hey, you're putting too much!" Sarah exclaimed.
"You need to eat! You're too skinny!" Lady yelled.
"That's more than enough! I can't finish all of these!"
"Sure, you can! Here! Get some more!"
"Wait, aren't these veggies?! You're just giving me your-"
"EAT!!! EAT!!!"
Maybe not completely on the same page. Still, they are getting there.
