This couple is not trying to conceive, which is why they chose this infertile day of her cycle to have unprotected sex.
Both photos are taken on the day before she began bleeding – you can see some fresh blood at the os. The first is pre-arousal. The second is taken about an hour later, after both male and female orgasm. You can see a pool of seminal fluid on the bottom. The cervix was much farther back in the vagina during the second photo shoot due to the ballooning of the vagina during arousal.
The sperm retention theory describes the cervical contractions and dipping in and out of the vagina as an evolutionary advantage of female orgasm. This theory posits that the rippling muscle contractions of the uterus and vagina during female orgasm shift the pressure in the uterus also causing the cervix to gape and suck (imagine a turkey baster if you rhythmically squeeze it). If the man has already ejaculated at this point, the dipping, gaping, and sucking movements of the cervix will help draw in the semen that is present in the vagina into the os and uterus (particularly if there is fertile cervical fluid present). If the speculum weren’t opening the vagina, the os would be sitting in a pool of semen.
Some say this theory is a myth. Check out this article about other scientific research on the role of the female orgasm.
Some fresh blood at os (she begins menstruation the following day)
Lubricated vaginal walls
Pool of seminal fluid below and covering os
Cervix deeper in the vagina than pre-arousal
Photo taken approximately 7 minutes after male and female orgasm