Shabbat 58a and Shabbat 58b, much about the badges slaves would wear, introducing two kinds of worries: the slave would lose the badge and adjust his clothing to cover the spot, in a way that made the garment no longer a piece of clothing but a burden, and/or would pick up the broken badge to carry it. From there, we got into issues of ritual impurity, how thought can make an item susceptible to it, but it takes an action to stop it, and what pieces of items are considered linked or not.
