[Papyrus's excitement is feeding Sans's, or something. Seeing Papyrus so amped up is definitely even more proof this was the right idea, at least. Sans's feathers all fluff up for a moment and he stretches them a bit--not too much; even with subconscious moments he's gotten used to not hitting things most of the time--before settling them again. It's not totally unheard of for Sans to wave a wing at Papyrus by way of greeting, especially when he's lying down and doesn't want to get up, but this is a much more excited motion than usual.]

I used your tools, but I bought the stuff to make it. The fuel's all sort of one-day only, just in some metal tubes. 'Course, you can definitely figure out how to make 'em more efficient, I mostly just slapped some stuff together until it caught on fire. [He's talking faster than usual, though it's not a match for Papyrus's enthusiasm. Still, notable.]