[groby_b]

Irrelevant - they talk about a technical issue they're familiar with. I can ask them questions about that issue. It's a good way to gauge their skill level while keeping them on familiar terrain.

It's usually fairly straightforward to see if somebody talks about their own experiences or is retelling a story they simply heard.

[TwistedWeasel]

Exactly, even if it's not their own story, if they are able to talk intelligently about the subject matter and explain the problem and solution well then i've gained valuable information about the candidate.

Unfortunately i've had a couple of candidates who's response to the question was "I don't really write bugs". Those are the ones I know for sure are lying.