Judging from the way Sans bursts out laughing, he quite likes "Pie", too. Papyrus lets out a heartfelt groan, but he's grown too accustomed to "Pap" to hold out any hope of correcting her.

Besides, Sophie's question is curious enough in its own right.

"Well, because Undyne told me to! It is very important to her that we capture a human! So if I bring one to her, then she'll finally let me be in the Royal Guard, and all the other Royal Guardspeople will want to be my friend!"

"and i've mostly gotta capture a human because, well, what else was i doing today?" Sans shrugs expansively.