Keep your cheeks and tongue tight. I ran flutes and resonance call for 20+ years before ever touching a short reed and I can tell you as long as the call is tuned properly, you should get correct goose sounds if you don't let you jaw or tongue or cheeks loosen up. Sounds easy right? Well try running a flute and then a short reed. You'll go crazy. In fact if you ARE running other types of calls and want to run short reeds, put those other calls away and just forget you own them until you MASTER the SR. It will do nothing but hinder your process. You might want to look into an instructional video or two as well. They helped me a ton.
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Don't do anything you wouldn't want to admit to the paramedics after.