Kenny McNeal from Bayou Bottoms indirectly taught me how. He does it and was sort of shocked when he asked me if I'd ever heard a big flock of teal on the ground calling at others and I said, "no". We hunted a bean field on the bayou de view that's usually rice. 
Finally one day at Mallard Lake there were thousands of GWT by my camp cackin away and I figured out why he did what he does.  
If any novice who reads this wants to learn as much as you can as quickly as you can I strongly suggest looking up Kenny and book a week with him if possible. (you'll need a group). 
Just do it.