Kunjal Kriya, in vernacular controlled vomiting, involves drinking warm, slightly salted water until the stomach is full and then expelling the water through the mouth.
For an untrained person vomiting is associated with disease and much unpleasantness. However, with training, this procedure become easy. The ability to conscientionsly relax parts of the body that is learned through long practice of Hatha Yoga is what makes this procedure easy.
Although the technique is simple, its mastery brings great benefits.
The main obstacle to mastering this technique is the perception of vomiting as something disgusting and even shameful.