Déjà vu is the strange feeling that you have experienced something before when you actually haven't. Scientists believe it happens when your brain's memory system briefly malfunctions, confusing new experiences with old memories.

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Yawning is contagious because of mirror neurons in the brain that make us automatically copy actions we see others doing. When you see someone yawn, your brain triggers the same yawning response, even if you're not tired.

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Hiccups happen when your diaphragm, the muscle below your lungs that controls breathing, suddenly contracts involuntarily. Most hiccups stop on their own within minutes, but you can try holding your breath, drinking water, or breathing into a bag to stop them faster.

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Static stretching (holding stretches) is better after exercise when muscles are warm, while dynamic stretching (moving stretches) is better before exercise to prepare your body. Stretching after exercise helps improve flexibility and reduce muscle soreness.

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Caffeine wakes you up by blocking adenosine, a chemical that makes you feel sleepy, from attaching to receptors in your brain. This allows stimulating chemicals like dopamine to keep you alert and energized.

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