Fingerprints; invisible ink; writing on one skin; x-rays.
Is One Allowed to Walk with Hiking Shoes or Anything Similar on a Dirt Ground on Shabbos?;
Making a Bruise or Using a Toothbrush When One's Gums Might Bleed. Using Floss, Toothpicks, and Dealing with Blood from a Cut;
Is There a Problem with Using Foods That Smear When One Is Not Going to Eat Them on Shabbos?;