Velvet Sparrow posted:

It means mama hen clamps her butt down tight on those eggs during the last three days, LOL. At that point she stops turning the eggs, which sends a signal to the chicks to rotate into hatch position. She feels the chicks moving around and locks down on the eggs, also once the chicks do the internal pip into the air cell so they can breathe, they start peeping--another motivator for mama hen to tighten her set.