The dude—William Bean, born 1909, died 1989—etched his first notch on his left thumbnail in November 1941, right before the U.S. jumped into WWII. Then he just… kept watching that thumb. Paper #1 dropped at the 10-year mark, #2 at 20, #3 at 25, #4 at 30, and the final one at 35. He knew his sample size was literally one thumb on one hand on one guy, but he couldn’t stop! Dude proved growth slows with age: from 0.123 mm a day at 32 down to 0.095 mm a day 35 years later. He also noticed nails basically hit pause when he got sick. Later studies? Pretty much same deal. #FunFact #NailCare