הלכה על ביצה 6:15

And that which we said that a creature is not neutralized and the intention was to say whether alive or dead - [that is] specifically a creature that is forbidden from the beginning of its creation, such as an impure beast or an impure swarming creature; and so [too,] a sciatic nerve, as it too is forbidden from the beginning of its creation. But a beast that is fit (kosher) from its beginning is only not neutralized when it is still alive - on account of living animals being significant and [so,] not neutralized (Zevachim 73a). But after it dies, it certainly [can have] neutralization; and we say that it [can be] neutralized, even with a large dead ox. And this is according to Rabbi Yochanan - as the law follows him - who said in the Gemara (Beitzah 3b) regarding significant things that are not neutralized, "We learned things that it is their way to be counted." [This is] meaning to say that we learned that the things that are not neutralized are those that it is the way of people to always count due to their importance, such as the seven designated above. But it is not the way of people to always consider an ox significant in their hearts; since it is not fit at the time, and [so] its benefit is not close to the hearts of people like those seven things.