I understand your doubt about contraceptive methods. The pull out method or coitus interruptus that you are asking about is one of the least effective ones. This is accomplished when during intercourse, the man pulls out his penis just before ejaculation. This requires much discipline. As orgasm is impending, a man may not withdraw in enough time to prevent semen from escaping into the vagina.
This method has a high failure rate, especially when the man cannot predict when he will ejaculate, or if he will want to have sex again within a short period of time, in which case sperm will probably be present in the pre-ejaculate.
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