"Inspection shall not be provided under subchapter 1 of this chapter at any establishment for the slaughter of cattle, sheep, swine, goats, horses, mules, or other equines, or the preparation of any carcasses or parts or products of such animals, which are not intended for use as human food, but such articles shall, prior to their offer for sale or transportation in commerce, unless naturally inedible by humans, be <denatured>"

What does this mean?

Basically that the meat used in all pet foods sold in the USA that contain meat (ie: almost all of them) must either be of such poor quality that it is already "inedible by humans" or must be "<denatured>" and that the FDA will not inspect such meats.