Maybe give shape another try.

https://www.youtube.com/watch?v=zHiWqnTWsn4

1:00:00 - Open/closed principle and 1:13:52 - Liskov substitution principle.

Both are given in terms of Shape, but it's to paint the picture that things are more complicated than you thought, even with something that should have been as simple as shapes. (As opposed to "shapes are easy, just model the world like that and it will be easy too")