i have mastured it in two different ways. the EASIEST way to do it is make a long chaaaaaaaaa noise with it. (consistant air being blew over the reeds). while doing that srtum your bottom lip like a guitar, you will make a gobble.

the second way it alittle better i think. consistantly blow air over the reeds, pretty hard. while letting your cheeks flap around wildly, shake your head side to side pretty hard. tell me how it works for you