Their footsteps still sound terrible, of course, but they come a little more quickly. She has reason and desire to follow him now, even if those are somewhat more in relation to his tone than his words.

"Sur...face...?" she murmurs to themselves with echoes of shock-confusion-glee-curiosity.

A few times, she'll almost seem to stop, the noises going silent--but if Sans looks behind himself, it'll still be keeping up closely.