We tend to think that we know our own bodies perfectly. We know how they work and what kinds of changes and processes are occurring in them every second of the day. But in fact, the human body is one seriously complex and mysterious mechanism that sometimes confuses even the most qualified specialists — doctors and scientists.
9: The cracking sound made by knuckles, necks, backs, and other joints when they’re cracked is the sound of bubbles popping in the joints’ fluid. Is it harmful? Not terribly. But cracking a joint too often can hurt the cords, called ligaments, that surround the joint
15: We give birth to over 200 billion red cells every day.