I believe I remember a story from Gerald that he and his dad used to net rabbits at night. Those who would scream little or not at all, were turned loose. Those who screamed to high heaven when held, would be taken back to the recording studio. After a few recordings they would turn them back loose. The number of screamers were few and far between, but when you got one it's all you needed.
This would fall right inline with what Byron is saying about the background noises.
Tony