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Oddly enough many social animals do this to some degree. Some species are social feeders like a lot of parrots, to get a finicky parrot to try a new food you can eat it or pretend to eat it infront of the bird. It's also a common behavior in primates, sort of a code of ethics. There've been studies on this showing that monkeys that dont announce a food source are often repremanded within the group.
As to why chickens do it, it could be any of those, or perhaps a sort of assistance call if the food source is too large to gulp down a pack of wild eyed hungry chicks to help break it up might be just the thing needed to consume the treat. The running and screaming might just be part of it.