"And also the carcass shall they halve" — the Mekhilta derives practical rulings about how damages are calculated when one ox kills another. The rule depends on the relative values of the two animals.
If an ox worth a hundred gored and killed an ox also worth a hundred, the owner of the dead ox takes half the value of the living ox. The damages are split evenly because the animals were equal in value, and a tam (first-time gorer) pays only half-damages.
If an ox worth two hundred gored and killed an ox also worth two hundred, the same rule applies — the damaged party takes half the living ox's value.
But the more interesting cases involve unequal values. If an ox worth a hundred killed an ox worth two hundred, the damaged party takes the entire value of the living ox — all one hundred. Half of the two-hundred loss would be one hundred, and that happens to equal the full value of the killer ox. So the owner surrenders his entire animal.
The most striking case: if an ox worth two hundred killed an ox worth a hundred, the damaged party takes only a quarter of the living ox's value — fifty. Half of the hundred-unit loss is fifty. Even though the killer ox is worth much more, the payment is capped at half the actual damage, paid from the body of the offending animal. These graduated calculations show how the Mekhilta built a complete damages schedule from a few verses of Torah.