Nedarim 25 - Tricks when taking an oath
Just as one can make a vow to motivate his friend to eat with him, and the vow won't be binding, since he only meant it for friendly coercion, so one can take a similar oath, which will be no oath at all, and he won't violate a prohibition of swearing falsely.
For example, one can say, "I swear, and let all the fruit of this world be prohibited to me, if I have not seen on the road as many as pilgrims going to Jerusalem!"
But perhaps he saw ants, and calls them "pilgrims," and is this swearing truly!? - No, that cannot be, because anyone who takes an oath does so on normal people's understanding of words, not on his terms.
But if so, why does the standard formulas mentioned "swear on our understanding, not on yours?" - That is to prevent incidents like the following. One person was going to swear that he returned the money to his fellow, who left it for for safekeeping. He put the coins in a walking stick, asked the depositor to hold the stick while he himself was holding the Torah scroll, and swore that he returned the money and that it was in the depositor's hands. At which the depositor became so infuriated that the broke the stick, the money fell out, and it came out the that man swore truly.
But did not Moses himself say, "Keep in mind that you swear today to observe the Torah, and do this on mine and God's understanding of this?" The Talmud then discusses all possible ways of how Moses could have put this into the oath to make the contract unbreakable, but finds ways to misinterpret them and to get out from under the obligation. In the end, the Talmud finds an unbreakable verbiage which is more complex though, so it tells that Moses just used the shortest way.
Art:An Old Woman Weighing Gold Coins by Rembrandt School