פירוש על קידושין 47:7

When the Torah uses one example to illustrate a law it can be seen as a paradigm for other potentially similar things. But when it uses two examples, it could be said that these examples are all that fit into the category. Thus it might be that the slave goes free only if the master puts out his tooth or eye.

The Talmud now demonstrates that both are necessary. The case of the eye teaches that he does not go free at loss of a milk tooth, which will be replaced by an adult tooth. And it taught tooth to demonstrate that he need not be born with the “limb” in order to go free at its loss.