Fingerprints; invisible ink; writing on one skin; x-rays.
Is One Allowed to Wash Windows on Shabbos? Cleaning Off One's Glasses;
How to Handle Confectionary Sugar When It Comes to Straining or Sifting;
How to Remove Gum, Paste, or Sticky Substances; Walking with High Heels on a Dirt Ground; Removing Twigs, Pebbles, etc. with One's Foot;