Wow, what kind of job? IIRC they're looking for stuff like breathing irregularities, heartrate change, body temperature... They ask you base questions, like your name and address so they get a measure of what you're like normally, then if they ask you a question and you lie those body functions are supposed to fluctuate and the machine picks up on that.
Personally I've never done one, but I think I'd fail just because I'd get all nervous with each question they ask me.
