Sans-Serif had actually noticed Duchess racing by when she'd first fled from the birds and into the castle. Of course he'd gone chasing after the strange white creature, in equal parts curiosity and concern. Curiosity because he'd never seen anything more tat fast that wasn't a him. Concern because he'd never seen the thing at all, but it had come from the direction of the aviary and the other him had always warned Sans-Serif not to go near there.

Once he'd stumbled across the little trail of dusty footprints, it had been easy enough to follow, though he'd had to follow somewhat slowly as his initial burst of enthusiasm had left him quite tired out. Not to mention that he still tended to trip and fall when moving much above a jog.

But eventually, the rattling of bones and the panting of a tired skeleton will probably become audible from just outside the throne room, until at last a small skeleton comes stumbling a little into view. He has to pause to lean on the doorframe, panting, and the first thing he notices in the room beyond is Frisk.

"frisk...i s-saw a thing...it looked like a scared thing..."