Undyne was in her home, teaching Papyrus to cook spaghetti when Sans teleported in and told Papyrus that there was a possible sighting of a human in the RUINS.
"Nyeh heh heh, I will finally capture a human! OUT OF MY WAY! I must capture this human!" He said, then rushed out of Undyne's home.
"Really Sans? I has trying to teach him to cook. Now this spaghetti is going to burn." Undyne yelled at Sans.
"Well then finish cooking it yourself. Either way, you were doing all the work." Sans said to her, slightly giggling after watching her try to finish the pasta.
After she finished making it, and throwing it away for whatever reason, she looked at Sans and realized that there hadn't been a human sighting since Chara arrived.
"Why did you really come? There hasn't been a human sighting in years."
"Well, I heard what happened to your eye, so I came to give you this eye patch, might intimidate your enemies." He said, then handed a handmade eye patch to her.
She took it and looked at it for a minute, pondering why Sans would do this. As soon as she looked up to ask him, he was already gone. She smiled and carefully slipped on the patch, wincing a little when she accidentally pressed it against her bad eye. She looked in her mirror and saw how mean she looked in it. Sans, thank you.
"Your welcome." She heard in her head.