Next they were supposed to walk into a curved single-file alley (it's also called a chute) that led to the squeeze chute. That was where the cattle balked. They just would not walk into the alley. It was the exact same alley feedlots all over the world were using without any trouble, so no one could figure out what the problem was. They couldn't see anything about their setup that was different from any other setup.
But to me it was obvious: the alley was too dark. The cattle were supposed to walk from broad daylight into an unlit indoor alley, and the contrast in illumination was too sharp. They were afraid to walk into pitch-black space.
That might seem a little surprising, since prey animals, like cattle, deer, and horses, usually like the dark. They can hide in the dark and feel safe, or at least safer than they feel during the day. But the problem wasn't the dark, it was the contrast of going from bright sunlight to a dark interior. Animals never like going from bright to dark. They don't like any kind of experience that temporarily blinds them, and that includes looking into a bright light when they're standing in relative darkness. I've found that cattle won't even walk toward a glaring lightbulb. You have to use indirect lighting at the mouth of an alley to make it work.
As soon as I saw the setup I figured that was the problem, and I confirmed my guess when I asked the owner how the cattle behaved at different times of the day, and in different kinds of weather. When he thought about it, he realized that the facility worked fine at night. Things weren't too bad on cloudy days, either. It was the bright, sunny days that were impossible, but no one had noticed the pattern.
I think a number of things are at work when an animal reacts that way. Cattle have excellent night vision and are used to seeing well in the dark, unlike people. So the experience of going temporarily blind in the seconds before their irises expand, which is something people take for granted, probably makes them panic. Also, cows don't live in houses with electricity and drive around in cars at night the way we do, so they don't develop a mental category called "eyes adjusting to an abrupt change in illumination." Last but not least, animals are so intensely sensitive to the visual world that I wouldn't be surprised to find out that sudden huge changes in illumination are physically painful in some way. People don't enjoy the experience of moving from brilliant light to a dark room, either, but for a cow it must be overwhelming.
Maybe when those cattle started to walk out of the sun into the chute they felt like they were going blind for real. They might have been having the same reaction you or I would have if we were driving down the street and suddenly went blind every time we drove through an underpass. If you went blind every time you drove through an underpass you wouldn't drive through underpasses.
I always tell people: whenever you're having a problem with an animal, try to see what the animal is seeing and experience what the animal is experiencing. There are lots of things that can upset an animal -- smells, changes in routine, exposure to things he hasn't experienced before -- and you should consider all of them. Anything in the sensory realm can upset an animal. But don't forget to ask yourself what your dog, cat, horse, or cow may be seeing that's bothering him.