It’s self evident to say that taking an exam is mentally taxing, but the physiological effects of answering exam questions are a news flash. In his book Thinking Fast and Thinking Slow psychologist Daniel Kahneman cites studies showing that our nervous system draws down the glucose in our blood when we are doing complex mental activity like test taking—just as we would from jogging. We become tired. And that makes us more prone to rely on impulse and gut feeling when we should be thinking through our answers. There’s a quick fix to this problem. Eat something. After 30-40 minutes of working through questions on the exam, snack to restore your energy levels. By doing that, you’ll be more deliberate during the exam, and your answers will more likely reflect what you do know.