We have learned (see above daf 5) that a woman with a veset kavu’a – a set menstrual cycle – need not be concerned that she may have become a nidda before seeing blood; she can rely on the fact that the blood is the indication of her status as a nidda. While few women can predict the exact date that they will menstruate, a veset kavua is established when a woman knows that she can expect her period to come if she menstruates on a consistent and predictable pattern (for example, when three consecutive periods begin on the same date of the Hebrew month).
On today’s daf we learn that there are other ways to establish a veset. Rav Huna teaches that occasionally a woman can perform a physical action that leads her to menstruate. For example, if on three occasions a woman jumps and subsequently menstruates, she has established a veset for herself and she can expect to menstruate after every time that she jumps.
Rashi points out that although Rav Huna gave the example of jumping, other out-of-the ordinary activities, e.g. carrying a heavy object or suffering from an illness, would lead to the same conclusion.
The rishonim offer different interpretations of Rav Huna’s ruling. According to the Ritva, Rashi and others, if on three occasions a woman jumps and subsequently menstruates, she has established a veset for jumping, regardless of the days of the week on which she jumps, and must anticipate that whenever she jumps she will become a nidda. The Rashba, Tosafot and others argue that the woman will only establish a veset for jumping if there is another factor involved. If she jumps three times on a specific day of the week and she subsequently menstruates each time, the woman will establish a veset for jumping on that specific day. Were she to jump on different days, however, she need not expect menstruation to take place.