This is an image taken from an MRI video of a couple having S%x.
The couple having s*x in the MRI machine is shown going through the Se#ual Response Cycle, which was originally researched by S*x therapists Masters and Johnson. The S#@ual Response Cycle consists of four phases that transition seamlessly from one to the next.
The second phase is “Plateau”:
Physical changes continue: Both partners experience heavy breathing, increased pulse, and muscle spasms. Changes in coloration will occur on the woman’s vaginal lips. For the man, the testes will rise and he will become fully erect.
Here is a view of the couple actually having $#x in the MRI machine.
The third phase of Masters and Johnson’s S#$ual Response Cycle Is :
Of the four cycles, this is shortest. The male and the woman’s and uterus tense. Women usually cannot reach as fast as men.
The fourth phase is “Resolution.”
The previous physical changes resolve; things return to their former state.
Masters and Johnson:
The Sexual Response Cycle discussed comes from a 1996 book called Human S$@ual Response By William H. Masters and Virginia E. Johnson.