Chewing Gum?
Students who chewed gum for 5 minutes before taking a test did better on the test than non-gum-chewing students. “Mastication-induced arousal” is credited for the boost, which lasted for just the first 20 minutes of testing. Many studies have shown that any type of physical activity before an examination can produce a performance boost; this study points out that even mild physical activity can bring on such a boost. Chewing gum gave the subjects multiple advantages, but only when chewed for five minutes before testing, not for the duration of the test, so you can’t chew gum and think productively at the same time.
Appetite, Jan 2012