Help students make the connection between functions and relations by relating a function to a toaster. Functions act like machines and in our lives, we expect our machines to work!
Toast, whether it's wheat or rye, should still come out toast. A bagel, wheat, blueberry, or otherwise, will still come out a bagel. If these items came out as a toaster pastry the machine wouldn't function.
This can be used to help introduce students to evaluating functions and the concept of functions in general.