Are you very knowledgeable in 3d graphics yourself, some of the replies here suggest that you may have a superficial knowledge (which is what I would have), if you choose an example domain that you have some knowledge about but not deep knowledge what happens if by accident your interviewee has significantly deeper knowledge than you? I worry that person might end up sounding overly technical or even like they're BS'ing their way through the interview.
There is also another way of creating 3D graphics that does not involve the use of faces and vertices, so developers with that background would be at a loss (or win depending on your viewpoint.)
