840. Activities Permitted During Twilight

Shabbos 24:9

One who protects his grain from birds or his vegetables from animals should not clap his hands or jump around as he does during the week. This is a preventive measure against the possibility that he may pick up a rock and throw it four cubits (about six feet) through the public domain.

Shabbos 24:10

Anything that is prohibited because of shvus (to encourage rest) is not prohibited during twilight (bein hashmashos). It is only prohibited on Shabbos proper and it is permitted during twilight for the sake of a mitzvah or in compelling circumstances. For example, during twilight one may climb a tree or swim through water in order to bring a lulav or a shofar. Similarly, one may remove an eiruv that he has made from a tree or from a carmelis (the quasi-public domain). If one is anxious about some issue, a shvus is permitted during twilight, but if something is neither compelling nor for the sake of a mitzvah, shvus remains prohibited. Therefore, one may not tithe produce that was definitely not yet tithed even though the prohibition against tithing on Shabbos is an example of shvus. One may, however, tithe produce of doubtful status (demai).