1) ''Building'' - ''Boneh'' - and ''Demolishing'' - ''Sotare'' - are both included in the 39 Avot Melachot (prototype prohibited activity).

1) At the time this Rabbinical enactment was instituted, most people had dirt floors in their homes; sweeping the floor would inevitably result in holes being filled, thereby improving the floor and constituting a violation of the prohibition against ''construction'' - ''Boneh'' - on Shabbat. In places where most people had dirt floors, it was forbidden to sweep even stone or wooden floors, so that people wouldn't make the mistake of thinking that it was permitted to sweep dirt floors. Nowadays, however, since people no longer have dirt floors, it is permissible to sweep the floor with a soft bristle broom (See Biur Halachah 337:2). 2) Even though it's generally forbidden to have a Gentile perform prohibited activities for a Jew on Shabbat, in this case, however, since the Gentile only intends to sweep the floor and not to level the holes, it's permitted. Although filling in holes while sweeping is inevitable, the Rabbis were not as stringent regarding the Rabbinical prohibition against asking a Gentile to perform forbidden work (See Mishna Berurah 337:10). 3) The feathers are so soft that only the surface dust will be moved around, but holes will not end up being levelled (Mishna Berurah 337:11).

אסור לכבד את הבית אפילו אם הוא מרוצף באבנים או בנסרים ועל ידי אינו יהודי מותר ואם עושה על ידי שינוי גדול כגון על ידי כנף אווז וכדומה מותר אפילו על ידי ישראל

1) At the time this Rabbinical enactment was instituted, most people had dirt floors in their homes; rubbing saliva into the ground served to level out the holes, thereby improving the floor and constituting a violation of the prohibition against ''construction'' - ''Boneh'' - on Shabbat. The Rabbis viewed this issue of rubbing saliva in the ground, as equivalent to the issue of sweeping the floor (see above). In places where most people had dirt floors, it was even forbidden, according to some, to intentionally rub saliva with one's foot onto stone or wooden floors, so that people wouldn't make the mistake of thinking that it was permitted to do so on dirt floors. Nowadays, however, since people no longer have dirt floors, the prohibition would not apply to stone or wooden floors (Mishnah Berurah 316:49,51 and Biur Halachah 337:2). 2) This leniency applies only if the saliva happens to be in one's path; in that case one may intentionally step on it (with the intent of causing it to be absorbed into the ground), without trying to spread it in any way. However, one may not intentionally go out of one's way and walk over to the saliva in order to step on it (Mishnah Berurah 316:51).