A broody hen has an overwhelming motherly desire to sit on and hatch her eggs. Some chicken breeds are more prone to broodiness than others. It usually takes 21 days for the eggs to hatch if they are fertile. Some hens don't seem to know this though and will sit on a nest for weeks on end. This should be discouraged because a hen will seriously neglect her own well-being while sitting on a nest of eggs. Some people discourage broodiness altogether (they may not have a rooster), so therefore the eggs won't be fertile. While a hen is broody, she will not lay anymore eggs.