Some people apparently use the thumb and forefinger to make the loop with their nondominant hand -- both are working from the same meridian; you need to make a loop by closing your thumb and pinky finger because you then have two different meridians and when the electrical circuit is broken, you have an accurate answer.
You then make a loop with your dominant hand -- thumb and forefinger this time -- more like a duck's beak. You will need to practice, but start by asking yourself a question to which you know the answer is wrong. Take your dominant hand loop and try to open your nondominant hand loop. If the answer is incorrect, the loop should open very easily. Next, ask a question to which the answer is accurate and correct and try again; you should not be able to open the loop of the nondominant hand.