Is it forbidden or not to have relations for the first time on Shabbat? There are two different versions regarding what Rav and  Shmuel held in its matter as it was known that one permitted and one forbade. If Rav holds like Rabbi Yehuda who prohibits "davar she'aino mitkaven" - doing a melacha when one was not intending to do that melacha, how does he permit (according to those who say he permits)? It must be that he holds that it is a destructive act and therefore permitted. Several sources are brought against Shmuel (who clearly holds like Rabbi Shimon that "davar she'aino mitkaven" is not forbidden) according to those who say that Shmuel forbade relations on Friday night for concern of bleeding. The first source is a Mishna in Nidda 64b that seems to indicate one could have relations on Friday night even if there is a likelihood that she may bleed from the tearing off the hymen. Rava resolves it by showing that in the case discussed, there is a decreased likelihood of bleeding as they already had relations for the first time and there is a chance she may bleed, but it is not clearly going to happen. The second question is from the groom's exemption from shema which lasts through Saturday night in the event that they did not have relations yet. Why would one be exempt on Shabbat unless one would be able to have relations? Rava and Abaye each provide answers. A third question is asked from a case of opening up a pimple on Shabbat which is permitted - why is that not the same as tearing the hymen?