Identity Oven
An oven that doesn't change what you put in is rebranded as the identity function.
Use this cartoon
Free for classrooms, worksheets, slides and other non-commercial use under CC BY-NC 4.0, with credit to Ben Orlin.
Cartoon by Ben Orlin, Math with Bad Drawings. https://cartoons.mathwithbaddrawings.com/2018-08-14-identity-oven/ (CC BY-NC 4.0)Transcript
A: "Your oven is broken. There's no heat. Put in cookie dough, and out comes cookie dough." B: "I call it... the Identity Oven!"