In an introductory note to this chapter, the Kitzur Shulchan Aruch writes that most Jews are already familiar with the prohibited labors of Shabbos and that he is only addressing common situations with which people may not be familiar. Clearly, the laws of Shabbos constitute an area requiring much greater study than this email alone will allow. 80:53 When a box or a utensil has flies inside of it, one must be careful to clear it out before closing it so that he does not trap the flies inside of it. One need not go through the whole item in order to ensure that absolutely none are left inside; just removing the visible ones is sufficient. (This only applies to a small box or chest; a fly would not be considered caught in, say, a closet – Mishnah Brurah 316:15.)
80:54 We may not draw blood on Shabbos; even sucking to draw the blood from one’s gums is not permitted. Similarly, one may not put a bandage on a cut in order to draw out blood (i.e., pressing it hard or wrapping it tightly to force blood out – Mishnah Brurah 328:147). One may certainly not squeeze a cut.