“It’s very rare for prey to suffer. “
I’m not so sure. I had a really dumb science teacher with a python about six inches across at the fattest point, who made a big show of feeding it live rats over the year so the class could see “science.” I only watched once, but that little rat’s tail and leg were going for I’d say 30 seconds to a minute or so. Maybe they have to be over a certain size or something.
Idiots in the class were so enthralled they wanted to get him a chicken and do it again, and the teacher said if they got him one he would do it. It wasn’t a pleasant sight, and I never bothered to look at any other times he was doing it.
Nerves... the prey dies quickly. What you are seeing is the nervous system shutting down. At that point, the prey is well dead.