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If someone takes an oath that something is different than what is known to be, this is a shevuas shav. For example, if someone takes an oath that a pillar of stone is gold, or that a certain man is in fact a woman, or that a certain woman is in fact a man, this is a shevuas shav.
It is interesting to note that although a person who takes such a shevuat shav will be liable to bring a sacrifice, had he taken a neder such as this, he would not be held responsible in any way, as we would assume that he is simply exaggerating, or speaking in a manner that is not serious.
A second new Mishna teaches us more about oaths said in vain. We are taught that vain oaths regarding oneself apply to both men and women, relatives and strangers, people who are qualified to testify and people who are not qualified to testify, inside of the beit din and outside of the beit din. If one transgresses, s/he is either lashed or s/he brings an offering. A person can put an oath on someone else if that someone answers, "amen" after the person has stated the oath.