(Mishnah): Sometimes one is liable for his ox' action and exempt for his own, and sometimes vice-versa.

If his ox caused embarrassment, he is exempt. If he embarrassed, he is liable;

If his ox blinded an eye or knocked out a tooth destroyed a tooth of his slave, he is exempt. If he did so, he is liable;

If his ox wounded his father or mother, he is liable. If he did so, he is exempt [from payment].

If his ox burned a stack on Shabbos, he is liable. If he did so, he is exempt, for he is liable to die.

(Gemara - Bar Padyei): All who ruin are exempt (regarding Melachah on Shabbos), except for one who burns or wounds.

(R. Yochanan): One who burns is liable only if he needs the ashes. One who wounds is liable only if he needs the blood.

Question: Our Mishnah says that his ox [that burned on Shabbos is liable to pay, i.e. in the same case that he is exempt because he is Chayav Misah. Surely his ox does not need the ashes!]

Answer: [Indeed,] his ox needs the ashes (e.g. it has a wound)! (MAHARA FULDA, SEDEI YEHOSHUA)