TThe scenery around them
"Oh yeah, Sans, what do you call these flowers?" Frisk asked. "These things? It's called an 'Echo flower'," Sans answered. "They copy what ever you say and stuff like that" Frisk got close to one Echo flower. She touched it. 'They copy what ever you say and stuff like that' The flower said. "See, told ya'" Sans said. He stood up and lend his hand to Frisk. Frisk held his hand and stood up. "C'mon princess, I'll show you something cooler than this," Sans said. "What could be better than this?" Frisk said. Sans smiled wider "You'll see" He said. "I go here if I feel alone or just hanging out" Sans said. "When me and Paps were young, we used to play here almost everyday. Well... all of that changed" He said. Sans' face darken. Frisk was curious but decided not to ask. She thought it would be too personal. "Here we are princess," Sans said. Frisk saw a beautiful waterfall.

"Go ahead. Explore, your prince will be waiting here for you" Sans said and winked at Frisk. Frisk gave him a warm smile. Frisk started roaming around the waterfall. She saw more Echo flowers, she touched one. 'BROTHER LOOK AT THE STARS!' The flower said. She touched another. 'Those aren't real stars bro' 'OH...BUT I ALREADY MADE A WISH'
'Really? Tell me' 'NO YOU WILL JUST LAUGH AT ME' 'C'mon just tell me. I promise I won't laugh' 'HMM...I WISHED TO SEE THE REAL STARS. I WANT TO SEE THE SURFACE' '*snort*' the voices...it sounds familiar. Frisk thought. She touched more Echo flowers. 'SANS!! YOU SAID YOU WON'T LAUGH!' Frisk wasn't surprised to hear his name. Sans, I knew it was them. She thought. 'Sorry Paps. It's just that's my wish too'. Frisk smiled. She went to the waterfalls and saw a duck. Quack quack. The duck said. "Oh, hello," Frisk said. "What are you doing here all alone?" Quack quack. The duck can only afford a quack. "Where's your family?' Frisk asked. The duck seems sad. Frisk gave the duck a warm smile. She carried the duck and brought it to the lake. "Swim little duck. You can find your family if you have determination. Be determined to find your family!" She said and let the duck go. Quack quack! The duck said happily. It swam fast through the waterfalls. Frisk sighed, "I wish I could find my family too..." She said.

~Sans POV~

"Go ahead. Explore, your prince will be waiting for you" I said. Frisk gave me a warm smile. That dazzling smile... I thought. She left me here. I walked around for a bit and remembered His wish...our wish. I closed my eyes and a picture appeared in my head.

(I love this GIF :3)

I smiled, remembering that time. Then, when I opened my eyes, I saw something familiar. A...ketchup bottle?. I picked it up and examined it."it looks like...someone was here..." I told myself. When I turned it, it has black goo stuff. How come I never noticed that?! "Crap..." I said and went to find Frisk.