Neither time is the answer that immediately springs to Frisk's mind. But they don't voice it. They're very good at not voicing things - there's a lot they've never told anybody, and the resets are at the top of that list.

Does Sans know?

He's always been weird, but they never seriously considered that he might actually know. They thought only Flowey remembered. Really remembered, not the kind of half-memories everyone else had and just as easily dismissed. Sans never said anything. He didn't even really act all that different the second time around, did he? They turn their head to stare uneasily at the empty bar. What else might he have known?

"I dunno." They pause for a second, weighing their words. "You only used to talk through the door - it was locked then. You didn't even know each other's names. But it was still important." It must have been. They remember finding Toriel's book of jokes in her room before they even knew what that meant, and Sans wouldn't have made a promise like that to just anyone. "You hang out a lot more now. Her name's Toriel. She's really tall and white."

After another moment of consideration, they add, "I guess she kinda looks like a goat."