Fingerprints; invisible ink; writing on one skin; x-rays.
הכנה ליום אחר (Preparations for a Weekday): Is One Allowed to Wash One's Hands Over Dirty Dishes if They Are in a Pan or...
Inserting Stuffing into a Couch Pillow, Detaching Connected Toothpicks, and Putting Back an Unattached Chair Seat or Cushion;
separating string cheese, yogurts, etc.