Horses often get 'cast' - that is - they lay down, then roll over too close to the wall. They wind up rolled up against the wall on their backs with their legs going up the wall.
Generally when people say 'cast' they're talking about a horse in a stall, but horses can also get 'cast' by rolling up against (or partly under) a fence outdoors.
But let's talk about in the stall. Since they're upside down, they can't get any traction on the fairly smooth stall wall, so they struggle and even flail around trying to get back on their feet, and there's nothing on the wall to help them.
A very high percentage of casting accidents cause life threatening injuries, shock, even death. Anything they get tangled in can provoke a panicked struggle. Until you have seen it, you can't BELIEVE what they can do to themselves or the structures around them. This is a blind, instinctive panic. You can't stop them.
If you try without knowing what to do and being very able bodied, you may get very badly hurt or even killed. We were taught to twist the neck up and hold the head to stop them from struggling but fat chance even getting in there and getting ahold of the head to quiet them - if it even works, I've seen it not work. We were also taught to get a soft rope around the hind legs and pull them away from the wall. Fat chance on that - it can actually make them get MORE panicked. A sedative can take too long to take effect- there just are no really guaranteed solutions - except to prevent it.
My (other pony, long ago) pony got his blanket over his head and struggled for hours - kicked loose a waterer line, so that was spraying all over and flooded the barn, and the (clueless) staff didn't notice it for several hours when they reported for work ('Hey, do you hear something bellowing and pounding and kicking?'). It was weeks before my horse could even walk normally, let alone work. He was one of the lucky ones - he survived. But he was in bad shape when they finally noticed him struggling away in his stall. A blanket strap had broken and was tied with baling twine. Baling twine NEVER breaks when you need it to. A stupid mistake like that can kill a horse.
There is one thing in this world a horse hates and fears more than anything - that is being in a position in which they are vulnerable to a predator. That means - losing its balance, feeling like it's going to fall, actually falling, and not being able to get back up, are things that terrify them.
Ironically, they may struggle so hard if they get cast, that they can actually kill themselves. But it is an incredibly powerful instinct and they will fight to the death to get back on their feet. That's why barbed wire is so bad - a horse can get tangled up in it and literally saw his own legs off struggling to get free.
The idea of the strips is that they can paw at the strips and get some traction on the wall. Then they have some chance of getting thir body pushed away from the wall. Not everyone agrees that they are effective, or worth the possibility of the horse getting stuck on them in other situations. I've heard some pretty hot and heavy debates of this product.....
Other methods of avoiding casting are piling straw or other bedding up against the wall to make a 'bank', in the old days, I'd occasionally see a wooden 'bank' that was made out of very solid wood, making a triangle shape with the wall and floor (same shape as the bedding 'bank').
Anything build around a horse has to be incredibly strong and absolutely hazard free. I've seen horses snap two inch thick planks like they were kindling wood. I've seen them kick through plywood and half saw a leg off when they hit the metal siding of a building and start ripping away trying to get their leg free.
A panicked 1200 lb animal who hates more than anything to be vulnerable to a predator, can in an instinctive panic, destroy all but the strongest structures, and then you have to think about the splinters, nails and screws flying all over the place. Designing and building a safe stable is a REAL challenge.
