Felldyne would join in, loud and proud. She’s an alto, her voice rich and resonant. She may or may not be known for being particularly rowdy when she goes out drinking, and the barkeeps that know her also know that it is better to direct that energy in a positive fashion, or there’s going to be a lot of broken furniture in the near future. Starting a round of singing is not a bad way to distract the Captain of the Underfell Guard.
I always see alot of Underfell Paps being worried of a sick Sans and being caring and tsundere as opposed to his usual tyranny. But I want to see is a grumpy sick Pap being told no to by a stern but worried-sick Sans.
So, somewhere, I’ve read about a headcanon which explained why Paps and Sans are mean to each other in the Underfell AU. What if they were mean to each other for protection. And at the end of the day they apologize to each other for doing so.