Gittin Daf 42

The Gemara concludes that if an owner knocks out his slaves tooth or blinds his slaves eye the slave is freed without any need for a shtar shichrur. If he knocks out another body part the master must write a shtar shichrur to free the slave. The reason for this distinction is because the tooth and the eye are explicitly mentioned in the text, as opposed to the other body parts which are derived from exegesis. Tosfos explain that even though exegesis is also considered Torah, nevertheless the slave requires a shtar shichrur because people who are ignorant of the law won't know that he is supposed to be freed and might question the status of the slaves children. We see from here the importance of going out of our way to avoid even erroneous misconceptions of our actions.