i would think that it is blood from mating attempts. my pair just mated and one of them bled rather profusely afterward, there was a small pool of blood after the mating had taken place. i am unsure as to whether it was the male or females blood, however i would not be surprised if there is gonna be small amounts of blood in the stool of one of them for the next week or so, due to local trauma to the area. unlike you hovever, my skinks are separated, and i only introduce them to mate. if i would you i would seriously consider separating your pair...it is not wise to keep them together all the time, especially at mating season, this can lead to excess violence and fights. also, if you separate them you can determine which one has experienced trauma...as long as they both continue to eat normally and their level of activity doesn't change much, than i don't think you need to spend money on a vet. good luck, hope this advice helps.