There are a few things you can do if you get stuck. The first thing to do is to stay calm and take a breath. Furthermore, you can take a moment to recap your thinking process so far and what you still need to find out in order to address the question at hand. If you are puzzled by some obvious contradiction, actively discuss this with your interviewer! Oftentimes an interviewer will wait for you to explicitly verbalize what combination of findings is puzzling you before gently giving you guidance.