"Serif!" They thoughtlessly leave off the 'Sans'--'Serif' alone is shorter, and they'll ask if he minds later. For now, they just beam--though there's a definite edge of concern.

"Was it her?" Frisk points at Duchess over their shoulder, taking a few steps in his direction just in case. Catching people might be one of their things now. "This is Duchess! She's a kitty!" Enthusiasm's still quite strong in their quiet voice.