They also use their feet to turn them. If you pick up a broody, rearrange her eggs a little, and put her back, you'll often see her scooching around on the eggs, and you can hear the eggs being moved under her, "scritch, scritch, scritch, scritch, scritch, scritch..." I think they turn them whenever they move around a little. If they have any poking out from under, they'll tuck them back in with their beaks.