Zevachim 72 - Why Nullification Does Not Apply
According to Biblical law, if forbidden food becomes commingled with permitted and is indistinguishable from it, and there is more permitted food than forbidden food, then the entire mixture may be eaten. This is the rule of nullification by simple majority. The Sages have introduced stricter rules, such as nullification of one part in sixty, but nevertheless the possibility of nullification in a mixture should exist. Why is it that a forbidden sin-offering, when mixed with permitted offerings, is never nullified, even one in ten thousand ?
The answer is that living creatures are considered important in their own right and are never nullified. But let us pull out an individual animal and say that since it came from a group where the majority is permitted, then we can presume that it is permitted! - No, this won't work. Since the animals are not really mixed but are standing, we cannot apply a rule of pulling from a majority. But let us make the animals move, then they will be mixed, and we will be able to apply a rule of pulling from a majority! - Sorry, but this is prohibited by the Sages, because people may mistakenly take an animal before they started moving.
Art: John Frederick Herring, Jnr. - A horse, pigs, ducks and cattle in a farmyard