You’re in a bubble of research.
There’s a clear sphere around the space you occupy that lets others look in, see what’s there. As with a lot of bubbles, there could be some distortion – from how you present it, from how they perceive it – but any sufficiently knowledgeable person can see in.
Like, say, your examiners.
Who are also in bubbles. Their bubbles might be bigger, they could be far away from yours – showing the distance between what you do and what they do – but they have them. And they’re reasonably clear bubbles like yours, open to inspection.
It’s essential you take a look before the viva. Read their recent publications. Check out their research interests to get a sense of what they do and how they might see things. Perfection and expertise are not essential: you just need to be aware.
In the viva your bubbles might collide, but not destructively. They’ll come into contact, and perhaps you can get a greater sense of how they see things. You may get idea for what you could do to improve your thesis, or look into in the future.
Bubbles don’t tend to burst in the viva – thankfully that’s where the metaphor falls apart!