Do you really need to drink eight glasses of water a day to stay hydrated? This physiology question intrigued the most readers, coming in as the most-viewed I Spy Physiology post for 2015. Exercise came in next, followed by cardiovascular health. Here are the top 10 posts for this year. Rankings are based on the number of views each post received. The metric is imperfect—posts published earlier in the year had more time to accumulate views, and views from the main page weren’t counted—but it’s a fun way to see what physiology topics caught your attention. The blog is not a year old yet, and we had a good showing already. Thanks for reading. Stay tuned for more physiology in 2016!