Many people take silence as a sign that they've made a mistake, or that the interviewer expects them to add detail. But trying to add detail to a finished explanation just makes matters worse for the candidate and can lead to verbal and behavioural confusion. So what should we do?
It's ok to remain silent. If two people stay silent, it often seems like a confrontation. Who will blink first? Who breaks the silence? And that's where body language has an important role to play. If someone is looking at you expectantly, then you can look back expectantly as well, perhaps with an open, attentive expression, suggesting that you want to hear what comes next. But don't take it too far - the interviewer might decide you have nothing else to say and politely show you out.
You can ask questions. You can interrupt a painful silence with an appropriate question. "Is there anything else you'd like to know?"
You can use humour. A touch of humour can be very efective - but it can also be counter-productive. Don't tell jokes, for example. But a sharp, witty comment can resolve tension. "They say that silence is golden..."
You can change the subject. Play a card, turn to a subject that you want the interviewer to know about. But do this with a strong opening line. "It occurs to me that there's something we haven't yet discussed."