This is a particularly hard case since its very hard to make canon reactions
( 80% - 90% ) accurate based on each character's personality
source :
undyne the undying fdy game
https://www.youtube.com/watch?v=VN4gebOuI48&list=PLDUwhYtCBMmydPjD0Y4JQT9ZWqY6lijb3&index=9
https://www.youtube.com/watch?v=nw-0JpDsW7w&list=PLDUwhYtCBMmydPjD0Y4JQT9ZWqY6lijb3&index=10