What are the signs of sour crop

I am not sure if I can tell you all of them...I just lost one of my Silkie's to sour crop and I missed alot of the S&S..her crop was large..did not go down for a couple of days it was large anough that I could see it..she was tired would not walk around very much. Then she vomited large amounts of green liquid...she had stopped eating and drinking...it was after I lost her that I realized what had happened.