Shabbos Daf 42 שבת דַף 42

Shmuel said that one may extinguish a piece of burning metal that is in reshus harabim so that the public will not be harmed by it but may not extinguish a piece of burning wood.

Rashi explains that the melocho of mechabeh (extinguishing a fire) does not apply to metal (since it merely glows). Although extinguishing metal was forbidden by the Rabbonim, they did not extend their decree in a case of potential damage to the public. Extinguishing wood is the melocho of mechabeh, and therefore it is prohibited in such a case.  

The Mishnah states that one is not allowed to place spices in a frying pan or boiling pot that were just removed from the flame but one may add them to hot food in a bowl or in a tureen where the food has been transferred.

Rashi explains that the bowl or tureen are a keli sheini (a secondary vessel) and a כלי שני אינו מבשל – a secondary vessel is not capable of cooking.

Rav Chisdah said that although one may not place a vessel under a hen in order to receive her egg (and prevent it from rolling off an incline) one may turn over a vessel and cover a newly laid egg so that it should not break.

Rabbah explained Rav Chisdah’s reasoning saying that the Rabbis allowed moving non-muktzeh items for the sake of a muktzeh item to prevent commonplace losses, but not for uncommon losses. Since a hen is likely to lay its egg in a trash heap, Rav Chisdah permits a vessel to be overturned to protect the egg from being crushed. He did not permit placing a vessel under the hen to prevent the egg from rolling off an incline since that is an uncommon situation.