“An average person may shed upward of 50 million skin cells a day. Attorney Erin Murphy, author of Inside the Cell, a book about forensic DNA, has calculated that in two minutes the average person sheds enough skin cells to cover a football field. We also spew saliva, which is packed with DNA. If we stand still and talk for 30 seconds, our DNA may be found more than a yard away. With a forceful sneeze, it might land on a nearby wall.” It turns out that we leave a lot of DNA in a lot of places, and once we leave it there, it’s doesn’t stay put. Which is really bad news if your DNA ends up, say, on a murdered man’s fingernails. The Marshall Project with some background on the science and the story of the man who was framed for murder by his own DNA.