When do chicks start to move inside the egg?

Chicks start to move inside the egg around day 18 of incubation. This movement is often referred to as "quickening". During this stage, the chick is starting to develop its muscles and bones and will begin to move around inside the egg. This movement can be seen as a slight twitching or jerking of the egg. As the chick continues to grow, its movements will become more vigorous. By day 21, the chick will be able to move its head, neck, and legs.