And now, Grandin's ready to begin her inspection. By the end of the morning, she'll know if this plant is mistreating the animals, or if the cattle are going to a calm and painless death.

"Let's just start looking at the truck unloading," says Grandin, "they're just unloading a bunch of cattle right now."

Grandin says the more she listened to cattle, the more she realized that their moos tell you how they feel. Photo: Daniel Zwerdling

From the outside, this slaughterhouse almost looks like a car factory: Semis keep pulling up to an unloading dock; there are windowless buildings, and smokestacks. But there's also a greasy, cloying smell in the air; and a labyrinth of fences and pens stretch from the unloading dock about a hundred yards to the plant.

Grandin walks to the rear of the semi, as it backs up to the edge of a pen. The driver hops out of the cab and opens the double doors. And steers pour down the ramp, like black boulders.

Grandin looks down at her clipboard, at the first item on her inspection list. She needs to stand here for a few minutes and count the cattle that go "moooo."

Or as her checklist describes it: What percentage of cattle are "vocalizing"?

Temple Grandin invented this system for inspecting a slaughterhouse. Nobody had ever done anything like it before.

"It's got to be simple," says Grandin. "You cannot have an audit with 50 different things to audit, where it would take the McDonald's auditor a week to do the audit. That would just be impossible."

So she studied thousands of animals, in slaughterhouses, and she looked for five crucial clues that reveal if they're calm or stressed. Grandin says the more she listened to cattle, the more she realized that their moos tell you how they feel.

"I just started checking off, 'Did the animal moo?' Yes or no? 'Was that moo associated with an obviously bad event?' And I found that about 98% of the cattle that mooed had a real good reason for doing it. I thought 'That's really going to work.' Vocalization scores separate a plant that has big problems from a plant that doesn't."

Grandin says this plant used to have problems: the drivers would shout at the cattle, to shoo them off the trucks. The cattle would get scared, and balk, so the drivers would shout louder, and the cattle would bellow so much they'd practically drown you out.

"One of the things that's been really important to the handling has been to get rid of all the yelling and screaming and whistling," says Grandin. "Cattle have got really sensitive ears and so one of the things I've worked on is getting people to keep their mouths shut when they're moving cattle."

But after decades of western movies—isn't that what cowboys do? They yell, they whistle.

"Well we need to get rid of that yelling, because it just gets the cattle all excited," explains Grandin. "In Canada, researchers have done two studies that found that yelling and screaming at cattle is really stressful. In fact, yelling and screaming does more to raise the heart rate than the sound of metal banging and clanging."

Grandin says this slaughterhouse has changed its ways. According to her inspection system, if only three percent of the cattle "vocalize," it shows that most of them are calm.

As these cattle are unloaded, all is quiet except for the sound of their hooves.

Temple Grandin is the most unusual crusader in a long line of Americans who've tried to make slaughterhouses more humane. Congress passed a law that forbids cruel practices, back in the 1950s.

But Grandin's own studies show that a lot of slaughterhouses ignore that. Around six years ago, she surveyed major meat plants for the U.S. Agriculture Department, and she reported that most of them did a brutal job of killing. Grandin says she also discovered that a lot of industry executives don't care, unless she can prod them to leave their offices and see problems.

"I remember the day one of the managers saw chickens. We had gone to a chicken plant and we found a live chicken in the garbage can," describes Grandin. "The people that were with me were really horrified. But I remember another time when I was out with some managers and we visited a hog farm and there was a half dead pig lying in the alley. He had been there for a good long time, and the manager leading the tour just walked our tour group right over the half dead pig. It's like they become totally desensitized and don't even see it. Bad had become normal."