I will add to this that I had a hen awhile back who ate a large amount of long grass clippings after I had mowed, and she got an impacted crop, which led to sour crop. She drank a huge amount of water trying to "wash everything down" and, as a result, was "gurgling" by the time I figured out something was wrong. I had to make her "throw up" several times to get all of the nasty liquid out of her, and she immediately stopped gurgling afterward. Beyond that, I gave her warm olive oil to help get the obstruction passed, and kept her on a diet of soft foods and yogurt for about a week afterward.
Check to see if your hen's crop is big and swollen up like a tennis ball or softball. She may have an impaction and a sour crop.
