Answer: If you are asking "What causes unstimulated ejaculation?" Then the answer is mental or unconscious stimulation. There is either a mental cue that releases semen, or some stimulation of the glans, the shaft of the penis,thetesticles ortheprostate that is not obvious to the individual. Now, post-coital release of semen is also common, sometimes for up to several hours after intercourse (manual solo or with a partner).
However, if you are curious about the possibility of pregnancy...
Sperm cells are constantly being produced in the testes. A single sperm is needed to fertilize an ovum, but the human reproductive system relies on thousands of sperm cells and several chemicals in semen to ensure that fertilization occurs.
Most men produce a decent level of testosterone through the age of 30. Testosterone is a hormone that is required to maintain healthy sperm cells. The older you get, the less healthy your sperm cells.
So, if your question is "can I get a woman pregnant during intercourse without ejaculation?" Then, the answer is yes, especially if you are less than 25 years old.
Answer: Because your vagina is an open cavity... This is normal.If you are trying to get pregnant, your are therefore advised to remain on your back after sex for a few more minutes, with your pelvis a bit elevated.