While exploring Cyber City with Noelle in Chapter 2, the player can encounter a hidden alleyway marked with dog signs. Going down this path results in Kris being run over and downed by the Annoying Dog, only for the Undertale game over screen to appear in place of the standard one. The Annoying Dog proceeds to run over that too, after which Kris and Noelle wake up beside a dumpster with a Dog Dollar added to the player's inventory.

This Easter egg nods back to a Tweet posted by Toby Fox in 2019, which consisted solely of the Annoying Dog's car sprite with the caption "this is the last thing you see before you die."
Contributed by game4brains
Attachment
Attachment
 
Video