This is a slight extension of yesterday's chapter due to a point I forgot to mention. If you're using a gym punching bag or one that will be used by others, make sure to wipe off the blood afterwards. It's just common decency.
Of course, the main reason is that you want to avoid people collecting such an exquisite sample of your DNA. With it, they would be able to do all sorts of mayhem including framing you as a murder suspect and cloning.