understanding the concept of "אין צובע באוכלין" (no coloring by food that's eaten)
understanding the concept of buying and selling
Using a Salt Shaker, Pepper Shaker, etc. on Shabbos;
Does It Make a Difference How One Removes Something Growing from the Body (e.g., Cutting vs. Biting Nails, Cutting vs. Plucking Hair)?;