Many hens will linger for a while in the nesting box if they feel like it for whatever reason. Broody hens, however, will never leave the nest, except to eat, drink, and release the most explosive, vile and fowl-er, I mean foul- smelling poo you have ever seen. Some will not get up at all!
When you try to gather eggs from a hen who is not broody, she may or may not give you a warning squawk, as if to say, "Hey, those are my eggs!" But, if your hen is broody, it will sound more like a violent shriek, hiss, or growl. Her intent is now not just a warning, but a threat. It means, "If you touch my babies, I'll rip your throat with my bare beak! GO AWAY!" If you are foolish enough to try to reach her eggs or touch her, your hand will be viciously attacked. She will puff up her feathers to make herself appear larger and more intimidating. When left alone, she will flatten herself in the box and stare off into space. Some have described it as a concentrated, zen-like expression.
It is a lot easier to get a broody hen if you have the right breed. Over the years, many breeds of egg layers have had the tendency to brood bred out of them. On a commercial egg farm, broodiness is a bad characteristic that is culled, because when a hen goes broody, she stops laying eggs as soon as she has a clutch. She will not resume laying until after her chicks are grown enough to reach independence from her. So, if you want a ton of eggs in as little time as possible, broodiness is a bad thing. Hens that went broody were culled, and the eggs from hens that didn't go broody were artificially incubated to produce a bird that almost never went broody.
Of course, there are always exceptions to the rule! Sometimes they will go broody no matter what their genetic makeup is, although if they are a breed that does not usually go broody and they do start setting (brooding), they may not be as good of a mother as a breed that usually goes broody. There are good broodies and bad broodies. A bad broody has little function in the flock. Because she is broody, she is not laying eggs, but because she is not a good mama, she may fail to hatch any chicks, or if she does manage to hatch them, she may not know what to do with the chicks once they hatch! Here is my White Leghorn who went broody once(she was not the best broody).
I still have all five of these chicks hatched by one of my Turkens. They are all beautiful adults now!
Breeds that will consistently brood: Old English Game, Silkie, Cochin.
Breeds that will probably brood: Australorp, Brahmas, Sussex, Shamo, Orpington, Naked Neck/Turken, Modern Game, Langshan, Aseel, Chantecler, Rhode Island Red, Dominique, Dorking.
Breeds that almost never brood: Leghorn, Ancona, Andalusian, Campine, Hamburg, Production Hybrids, Minorca.
This list is not all-inclusive but it will give you a place to start!