Sotah, Chapter One, Mishnah Seven
This mishnah and those that follow are about the concept measure for measure. The Sotahs humiliation and punishment fits her crime of adultery.
In the measure with which a person metes out to others, they mete out to him.
She adorned herself for a sin; the Omnipresent made her repulsive.
She exposed herself for a sin; the Omnipresent exposed her.
She began the transgression with the thigh and afterwards with the womb; therefore she is punished first in the thigh and afterwards in the womb, nor does all the body escape.
According to the theology of this mishnah, God acts upon a person in relation to that persons actions. So too, the Torahs punishments for the Sotah are commensurate with her crimes. The mishnah now illustrates this. She is made repulsive, her clothes are ripped and her hair is torn, in response to her adorning herself in preparation for adultery. She is exposed for all to see, because she exposed herself to her lover. Finally, the Torah states that if the waters find her to be guilty, her thigh and then womb (belly) will be disfigured. These are two of the areas of her body that were involved in the affair. She exposed to him her thigh, which is often understood to be the genitalia, and then she allowed him to enter her womb.
The mishnah notes that this is only the beginning of her curse. She should not think that only her thigh and belly will be disfigured. Rather they are just the start.