Shabbos 24:4-5

Shabbos 24:4

One may chop gourds for cattle and a neveila (an animal that died without ritual slaughter) for dogs. Rabbi Yehuda says that this is prohibited if the animal was not a neveila before Shabbos because then it was not prepared for this purpose.

Shabbos 24:5

Vows may be annulled on Shabbos and one may inquire about things needed for Shabbos. One may plug a hole that admits light (to prevent the spread of ritual impurity), and one may measure a piece of cloth that came into contact with vermin (to determine if it is impure) and a mikvah (to ensure that it is large enough). An incident occurred in the days of Rabbi Tzadok’s father and Abba Shaul ben Botnis in which a light-hole was plugged with a pitcher and a pot was tied with grass in order to determine the size of a breach (vis-à-vis the spread of ritual impurity). From the fact that they permitted these things, we derive that one may plug, measure and tie for mitzvah purposes on Shabbos.