Rehearsal, Not Run-through
A mock viva is rehearsal for the viva but not a run-through. It’s important to grasp this. There are no scripts to learn but there’s a mood to appreciate. You can’t know the right words in advance but you can get a sense of the tone and the process.
Your supervisor and anyone else involved will try to give you an experience that feels like a viva. They’ll ask relevant questions and make comments to simulate a typical viva but ultimately it won’t match the real one that you’ll eventually have.
It’s a rehearsal, not a run-through. If you understand and accept the purpose then a mock viva is probably one of the most valuable activities you can engage with to help your viva preparation.