Frisk snorted and leaned back in her chair with a grin. As Sans continued to eat, she grabbed her soda and took a couple gulps of it. In the middle of that, she heard Sans' loud slurping sounds and tilted the bottle down. She raised an eyebrow curiously. Was that supposed to be a challenge?

She smirked. Challenge accepted!

After setting her soda back down, Frisk picked her fork up and prepared another bite of spaghetti. She looked Sans in the eye as she slurped up the noodles, louder than he had before. Her inner, well-mannered adult told her to stop. She knew better than this!

But she couldn't keep herself from smiling and giggling. Who cared if anyone would find offense in their little challenge? It was fun! 

Determined to win, especially since she was the only one with actual lips there, Frisk took another bite. She slurped the noodles up as loud as she could. While she achieved her desired effect, she ended up being cut off by a sudden cough. She laughed through it as she grabbed her napkin and covered her mouth. 

"Okay...Okay, you win," she said, continuing to laugh.