I just wait until they lay an egg, but if you put them back and they go back to brooding you know they're not broken and you should try again for 3-4 days. 

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My girls tend to do a lot of "growling" during broodiness when you touch them, try to pick them up or even around the other hens when wandering around. So a good clue for me is when they stop this growling, then I know they are done with the broodiness. This growling also happens about a week before they actually start in with the broodiness, so I know it is coming on.i have a related question i've been trying to get answered (sorry for hijacking). if you use the cage method to break a broody, how do you know when it's worked? i have a hen that i want to break, she isn't being terrible, gets up to eat and drink, but i don't have any roos, or room for any more chicks this year, and i want her laying again.
thanks