853. Nullifying a Utensil's Usefulness

Shabbos 25:22

If straw is on a bed, it may not be removed by hand. Rather, one must move it using his body. If the straw can be used as animal feed, one may to carry it by hand. Similarly, if a pillow or bedding was placed on the straw, it's as if one already sat on it before Shabbos began and it may be moved by hand. If a person brought a vessel full of soil into his house, if he designated a place for it on Friday, he may carry it on Shabbos and use the soil for his needs.

Shabbos 25:23

It is prohibited to nullify the usefulness of a utensil on Shabbos because doing so is tantamount to destroying it. For example, one may not place a vessel below an oil lamp on Shabbos in order to catch the dripping oil. Since the oil in the lamp may not be carried, dripping into the vessel will cause a utensil that had been permitted to become prohibited   This applies in all comparable situations. Because of this, a dish may not be placed beneath a chicken to catch the eggs that it lays, though one may cover the eggs with a utensil. One may likewise use an overturned utensil to cover anything that may not be carried on Shabbos because doing this does not nullify the utensil's usefulness. If one wants to take such a utensil, he may do so.