US State Department issues updated travel advisories for these countries: See the full list

Detailed Explanation on Instagram: "Follow @detailedexplanation to learn something new every day! 🧠 When you raise your arms, the veins in your hands and arms have to work against gravity to return blood to the heart. Unlike arteries, veins don’t have strong muscular walls to push blood forward, so they rely on a combination of valves and external forces. Tiny one-way valves inside the veins stop blood from flowing backward, while the contraction of nearby muscles squeezes the veins and helps p