That is concerning. After tensing very slightly, Frisk gently reaches over to run a hand down his spine.

"Yeah. S-4 is great. We've both got good family here, even without moms."

They're pretty good at getting a read on people, even if those people aren't what most might consider 'people'. So they can sort of get a feeling that the cat mother might be...projecting, now that she's alone. After a pause, they reach over to pat Duchess' back, too.