Then the priest shall say unto the woman. These words are parenthetical, just as in Matthew 9:6. The latter part of the oath is called "an oath of cursing," because it contained the imprecations on the guilty.
To rot. Hebrew, "to fall." τὸν μηρόν σου διαπεπτωκότα,, Septuagint. To swell. The Hebrew zabeh is not of quite certain meaning, but probably this.