What was one of the techniques leonardo used to create the illusion that the mona lisa was a real person

He used the practice 'sfumato' which he described as "without lines or borders, in the manner of smoke or beyond the focus plane". This was the main technique/practice that he used in created the mona lisa, so I assume that it is probably the most relevant to your answer :-)

Gouges, because, like there named, they gage the amount of space an object has to move around.hope this : )