Writing with something permanent on a material that is permanent.
Understanding the Difference Between ממצא חפציך (Mimtzo Cheftzecha), דבר דבר (Dabair Davar), and הכנה (Hachana);
Sprinkling Water on a Carpet. Asking a Non-Jew to Wash Your Floors;
The halachas of opening food packages with letters, numbers, pictures.