The puffy vulva is also ideally shaped so that the tip of the male's penis can easily hook into its fold to be directed into the vagina during copulation. During copulation the male thrusts his penis into and out of the female's vagina while shifting his weight from one leg to the other in order to work his bulbus glandis into her. This locks the male's penis into the female's cervix, which undulates to stimulate his penis to erection. Erection expands the bulbus glandis and ties the two
Wolves together; thus coitus is achieved. Once coitus is achieved, the female's vaginal sphincter muscles tighten around the male's bulbus glandis to hold it firm as she pulls forward, triggering ejaculation of semen into the uterus. In the initial 30-50 seconds of the tie, the male deposits only clear semen until orgasm is achieved. During the initial 30 seconds or so of orgasm, a cloudy, somewhat thicker, sperm bearing semen is ejaculated; thus insemination is achieved. After insemination the semen returns to a clear state, but continues to pump forth until the end of the tie, which may last up to 35 minutes.