 The dog's penis enlarges inside the vagina, thereby preventing its withdrawal; this is sometimes known as the "tie" or "copulatory lock".The male dog rapidly thrust into the female for 1–2 minutes then dismounts with the erect penis still inside the vagina, and turns to stand rear-end to rear-end with the female dog for up to 30 to 40 minutes; the penis is twisted 180 degrees in a lateral plane.During this time, prostatic fluid is ejaculated.