"Oh my god! Look at that, there's already more dragons," Papyrus exclaims, as though the second dragon is proof enough of his tadpole-like marine dragon theory.

The odd reflective quality of the art grabs his attention, especially given that the picture's already scuffed - how much more reflective would they have been when first made? Despite the amnesia, his puzzle senses are tingling.

With a little prestidigitation to light one of his torches, he tests holding it up at various angles, both to check for any fine details, and - perhaps more importantly - to see if the light reflects off in any direction to make anything glow. You know, like a good old fashioned mirror puzzle.