פירוש על קידושין 31:15

If the female slave goes out at her father’s death, then the mishnah should have listed it.

The Talmud resolves R. Hoshaya’s difficulty by saying that the mishnah simply omitted one way a female slave goes free.
The problem is that according to talmudic thinking, the mishnah would not just omit one detail—it must omit at least two.
The first suggestion as to the other detail it omits is the death of the master. But the problem with this suggestion is that a male slave also goes out at the death of his master. So this is not a way in which a female slave goes out that a male slave does not.