We'll list three types of—what is a vain oath? Number one: A person takes an oath that contradicts something that's known to people. For example, he says that a stone column is made of gold, or that a man is a woman, or that a woman is a man. These are obvious cases that are directly contradicted by a person's knowledge and sight. He knows what is what. So therefore, he's obviously swearing about nonsense. That's an example. The second type of example is when he swears about something that's impossible.
For example, a person says, “I swear that all the fruits in the world should be prohibited to me if I did not see a camel flying in the air.” The person's intention here is to really show that he saw a camel flying in the air. He's so strong about it that he's swearing that all the fruits are going to be prohibited to him if he's wrong. And obviously, he can't see a camel flying. Or he says, “I swear that all the fruits in the world are going to be asur (prohibited) to me if I did not see a snake that had streaks on its back like an olive press.” The back of an olive press has ridges on it. Obviously, the snake is smooth on top. And when a person made that swear, it was an obvious lie. That's the second example of Shevuat Shav (vain oath): impossibilities.
Thirdly, a person speaks to witnesses who knew certain things about somebody that would be helpful to him in court and tells them, “Please come and testify for me.” They reply, “Shevuah, we're making a shevuah—we're making a swear that we're not going to testify for you.” That's another example of Shevuat Shav. Why? Because they took a swear to violate a mitzvah (commandment). There's an obligation from the Torah for witnesses to testify if they know information that would be helpful to somebody and he's asking them to come to court. So they're violating a swear against the Torah. So therefore, that swear does not take place, and it's a Shevuat Shav.
If a person made a swear not to make himself a sukkah (booth)—that means, to live in a sukkah during the holiday of Sukkot—or not to carry a lulav (palm frond) on Sukkot, or not to put on tefillin (phylacteries), Chas veshalom, he's also guilty of Shevuat Shav. He can't take a swear against the Torah. That's a swearing for nothing.
Zo hi shevuat shav shechayavin al zedonah makkot (lashes) ve'al shigegatah patur. These are all examples of a Shevuat Shav, where a person who made these swears on purpose would be obligated to receive makkot, malkut (lashes), for violating the prohibition. And if he did it by mistake, there's no punishment.
Like we said, it's different from a Shevuat Bitui, a swear when a person prohibits something on themselves or they swear about something that happened in their past. In that case, if a person did it by mistake, they would be obligated to bring a korban chatat (sin offering), a oleh v'yored (variable offering), but here, there is no punishment for violating the swear unintentionally.