I once talked to a guy who had a Halal chicken processor as one of his customers.
You are correct. He said that they would bring all of these chickens out into a penned area, and then turn on a tape of an Imam praying. Then the bloodletting would begin. They’d start slitting chicken throats and letting them bleed out just as fast as they could go. For once that prayer ended and the speakers fell silent, they had to stop.
Weird!
Practice makes perfect.