Dr. Temple Grandin has written a piece on shechita for the Jerusalem Post:
NOW THAT I was able to hold the animal gently, it was possible to observe its reaction to shehita. When shehita was performed on each steer, I was amazed that the animal did not move. To find out if shehita was really painless, I started holding the head of each animal with less and less pressure to see if it would move during shehita. Even big bulls stayed still when the head holder was so loose they could have easily pulled their heads out.
I also observed that some shohets were better than others in their ability to cause rapid unconsciousness. All of the cuts were correct from a religious standpoint, but some shohets were more biologically effective. A swift cut was more effective than a slower one. In the hands of the best shohets, the animal does not make a sound or flinch, and drops unconscious in eight to 10 seconds.
My experiences in seeing how humane shehita can be could not have prepared me for the video taken at the kosher meat plant AgriProcessors, which recently became the center of considerable controversy. The video showed cattle that were clearly conscious after their throats had been cut and their trachea had been ripped out and was hanging from their necks.
I have been in over 30 kosher plants, and I had never seen such a dreadful procedure. Obviously, yanking on the trachea would cause great pain and may have delayed the onset of unconsciousness.
She also notes that many of the South American plants that export beef to Israel [and the US] also have serious problems. [Much of this meat comes to the US with OU and Satmar-related supervision and is used in OU products and restaurants, MealMart, Alle Processing and Schrieber's.]
Read it all here.