A shadow can be bigger than the object that casts it. Depending on the light, the distance, the angle, it might not be clear what the object even is if you only look at the shadow. Edges can be blurred, and perfectly normal things can seem scary from a glance at a shadow.
When you look to find out more about the viva, are you looking at the viva itself, or a shadow? What you see might depend on another’s experience, on the rules of your institution, on how you’re feeling that day about your research, and on many other factors.
Make sure when you find out about the viva that you get as full a picture as possible. Look for more than shadows. Build up more than simple impressions. Then you’ll be able to prepare well.