The Tempo
Pause when your examiners ask a question or make a comment.
Use the time to think and get your thoughts in order.
Remember that you might not have an answer but you can always respond.
And also remember that pause, think and respond has a tempo that you can use for every question, not just the tough ones.
PS: want to find out more of what to expect at the viva? Then check out the latest issue of Viva Survivors Select, The Expectations Issue. Twenty posts from the Viva Survivors archive plus two new pages of viva help exploring what the viva is like.