"צביעה באוכלים" (coloring in foods) - the stringent view of some poskim
Washing Off an Item That Has an Insect on It (e.g., Utensils, Fruits);
understanding the concept of מטה של פרקים (a bed used to travel that had to be put together and taken apart);
Is There a Problem with Using Foods That Smear When One Is Not Going to Eat Them on Shabbos?;