Muskets used up until the Civil War were smoothbore. Then, it was discovered that by cutting spiral grooves into the barrel (rifling), accuracy could be greatly increased. We generally think of blood vessels as straight tubes like water pipes. But, they actually have a slight twist to them. This “gentle corkscrewing” makes blood flow more effectively than smooth tubes. It helps regulate surges in pressure and is especially valuable at T-junctions to make sure the blood “turns” the right direction. It also helps prevent clogs. What incredible design from a brilliant Designer! Just one more example of how we are “fearfully and wonderfully made” and not just a bunch of random, lucky chemical accidents.
New Scientist 158(2134):19, May 16, 1998.