Baseball stitches that hold the two identical halves of a baseball's horsehide skin together permit the pitcher a better grip and also contributes to curve balls.  As the curve ball spins, the velocity of the skin relative to the air surrounding the ball on its path is different on opposite sides of the ball, creating a slight vacuum altering the course of the ball.  You can shape your hands and fingers to simulate the special curvature of a baseball skin and seems.\n\nThe baseball skin was invented in my home town of Stoughton, Mass. where I believe they were going to erect a suitable monument at one time.  At the baseball Hall of Fame in Cooperstown, I saw only a small faded news article, within a glass case filled with the oldest baseballs, that even mentioned the invention.  I'm glad you asked.