As with any personal gain spell, there is a backfire: the caster has to speak the truth to anyone as well. The spell lasts for twenty-four hours after which all memories of that period are erased. Only the caster will remember all that is said.
In 1998, Prue Halliwell cast this spell to find out what her boyfriend, Andy Trudeau would truly think when she told him that she was a witch. When she told him, Andy couldn't accept it. However, when the spell wore off, he forgot. Prue broke up with him anyway, thinking that it would be better to end the relationship now instead of later.
Later, when Andy discovered that Prue was a witch, she told him about the spell and it turned out that Andy was fine with Prue being a witch. But he told her that no matter whether he had a minute, a month, or a year to think about it, his decision would have been the same. He wanted to have a normal life to come home to with a white picket fence, a two car garage, a screaming kid, but no demons. Andy said that it could be because of all the evil he dealt with everyday on the job. Prue understood, knowing that she wanted exactly the same thing, but she can't. 
A few years later, in 2003, Paige Matthews had cast this spell for the same reason as Prue did. She was dating a guy named Nate Parks. Paige thought, since he had a Celtic tattoo, that he might accept her as a witch. Paige saw a future with Nate and thus cast the spell. However, she found out more than she wanted to know. Nate was very accepting of Paige's magic, but he also revealed that he was married and had two children. Paige immediately broke off their relationship and, in order to protect their secret, asked Darryl to put him in the local jail. Darryl, with great reluctance, did so and kept him there until the spell wore off.
Later that day, Paige cast the spell again on her grandmother, Penny, so that she would reveal her true feelings for The Necromancer. Grams revealed that she still loved the Necromancer, but that her love for her family was much, much stronger. She then vanquished the Necromancer. The next day, a confused Nate was confronted by Paige, who broke up with him again, as he had forgotten the events of the previous day. 
- For those who want the
- truth revealed,
- Opened hearts and secrets
- From now until it's
- now again,
- After which the memory
- Those who now are
- in this house,
- Will hear the truth
- from other's mouths.
Notes and Trivia
- In "Ex Libris", Prue wanted to use the spell to make Gibbs confess the truth about murdering Cleavant Wilson's daughter, Tyra Wilson, but Phoebe talked her out of it because good witches weren't allowed to use magic to punish the guilty.
- A shorter version of the spell was used in season 5 which left out: Those who now are in this house, will hear the truth from other's mouths.
- Prue and Paige used the spell for the same purpose: to find out if their boyfriends could accept them being witches.
- There is also a potion which works the same way as the spell does. It was used by Paige in "Vaya Con Leos", though nothing is known about it.