I do it like this;
Start with my tongue between my lips with alot of pressure behind it. It's like trying to spit something off the tip of your tongue. As you retract and drop your tongue, the pressure is released, causing immediate break in the reed. Use just enough pressure NOT to lock the call. Once breakover has been reached, back off on the pressure. There you have it. Pretty simple really. If you really are looking for a reference word, "T-Haww" would be the one I use.The spit note can be hard for many to learn, but once you've got it, it's very easy.
Remember, hand control also plays a factor in this call sounding right. Keep your hand fairly tight for the initial burst of air, then open up to allow the "Haww". Keep practicing and you'll get it.
Causing permenant flight delays
Callin' 'em in and knockin' 'em down