Fingerprints; invisible ink; writing on one skin; x-rays.
Different Halachas Regarding the Use of Slotted Spoons and Regular Spoons;
Is there a problem with unfolding clothing (e.g., TALIS, pants, etc.) on Shabbos and folding a paper napkin on a line;
How and when is one allowed to squeeze or suck the juices from fruits straight into one's mouth.