I had recently published a (terrible, but also terribly fun to write) JavaScript physics engine, which the interviewer saw on GitHub. He began with, "how does it work?" and then continued with probing questions, getting deeper and deeper into the various problems I solved while developing the library, especially focusing on tradeoffs between various choices.

By opening the discussion on "my turf," he put me at ease in the conversation, but by driving the interview with very technical questions, he also got the answers he needed about my technical ability.