Sotah Chapter 3, Mishnah 4. This mishnah deals with the curse actually taking effect, and also with cases in which it appears that the curse is not being fulfilled.
The curse taking effect:
"ein hamaspeket lishtos" - she does not even manage to finish drinking.
"ad shepaneha morikos" - her face takes on a green or yellow tinge.
"v'eineha bolotos" - her eyes begin to bulge.
"v'hi mismale'is gidin" - her body swells until it appears full of veins, and the veins protrude and bulge outward.
"v'hem omrim: hotzi'uha, hotzi'uha - shelo t'tamei es ha'azarah" - those standing there, seeing these things happening to her, give instructions to remove her at once, so that she should not defile the azarah, the courtyard of the Beis HaMikdash, out of concern that she will become a niddah as part of this affliction.
In practice she is not standing in the azarah itself, but at the Gate of Nikanor, which leads from the Women's Courtyard into the azarah. Even the concern that she may die is not the problem, since a dead body is permitted to be at the Gate of Nikanor and from there outward. However, a niddah - and likewise a zavah, a zav or a woman after childbirth, all those whose tumah came from their own body or who are tamei on account of something that came from their body - may not be anywhere on the Temple Mount, including the Women's Courtyard. Therefore they say to remove her from there before anything happens.
The merit that suspends:
The mishnah continues: "im yesh lah zechus - toleh lah" - that is, the merit suspends the punishment on her behalf, and she will hold up and not die. The Gemara explains an example of such a merit: that she took the trouble to bring her children to learn Torah, or that she waited for her husband while he was out of town in order to learn Torah. The merit of Torah prevents her from dying from the waters of the sotah, even if she is genuinely guilty.
And the length of time the merit suspends varies:
"yesh zechus toleh shanah achas" - a merit that suspends for her one year.
"yesh zechus toleh shtei shanim" - a merit that suspends for her two years.
"yesh zechus toleh shalosh shanim" - and sometimes even three years.
Teaching Torah to daughters:
The mishnah says: "mikan amar Ben Azzai: chayav adam l'lamed es bito Torah" - from here Ben Azzai learned that it is fitting for a daughter to learn Torah, so that if she drinks and nothing happens to her even though she is guilty, she will know the idea that merit suspends, and that this does not prove that she is free of sin.
Rabbi Eliezer disagrees with him and says that whoever teaches his daughter Torah, it is as though he teaches her tiflus. This is because he held that the learning gives her a measure of cunning, and enables her to operate in a way that is liable to bring her into greater contact with men.
Rabbi Yehoshua adds that a woman, and particularly a married woman, prefers one kav - a certain unit of measure, meaning a minimal amount of physical food - along with the tiflus, provided that her husband is available to her for intimacy, over nine measures of physical food that come with separation and distance from him. In other words: if something would cause her husband to earn a great deal of money but be out of town, she prefers that he be in town and earn less.
Three who bring ruin to the world:
Rabbi Yehoshua would say that there are three types of people who are problematic:
A foolish pious person: a person whose piety is foolish - for example, a woman is drowning in a river and he does not save her because he does not want to look at her.
A cunning wicked person: a wicked person whose wickedness is not apparent on the surface; rather, he carries out his deeds with great cunning, in a way that he still appears to be righteous.
An abstinent woman: a woman who presents herself as ascetic and pious when she is nothing of the sort, and in fact makes use of witchcraft. This phenomenon was common in their days: people who would present themselves as ascetics and flog themselves, but all of this is external activity only, which does not testify to genuine piety.
All of these bring ruin to the world, because they are not what they appear to be.