Admit It When You Don't Know Something
It is usually a mistake to pretend to know something that you do not, because chances are that the interviewer will follow up with questions regarding that exact topic. If the candidate cannot answer these follow-up questions, it tells the interviewer either a) the candidate does not know his/her stuff, or b) the candidate lied about knowing the topic. Either way, it is a big turn-off.
It is usually a mistake to pretend to know something that you do not, because chances are that the interviewer will follow up with questions regarding that exact topic. If the candidate cannot answer these follow-up questions, it tells the interviewer either a) the candidate does not know his/her stuff, or b) the candidate lied about knowing the topic. Either way, it is a big turn-off.