Don’t Prepare Monologues
Your examiners are not attending a play. They don’t want you to sit (or stand) and talk at them for hours. They want a conversation. They want you to respond rather than recite.
There might be tricky parts of your research or thesis where it matters if the words are said a certain way. Of course, check that you remember them correctly – but don’t expect to simply parrot them to your examiners.
It’s far better to have general rehearsal for responding to questions (with a mock viva or having a chat with friends) than it is to write down and try to memorise lots of possible responses to lots of possible questions.
You need to talk in the viva. You need to prepare to do that. You don’t need to have prepared responses or monologues.