To grasp the concept of dog-on-dog knotty relationships, it's essential to understand the basics of canine copulation. When a male dog mounts a female, the bulbous gland located at the base of his penis, known as the bulbourethral gland or "knot," becomes engorged with blood. This swelling causes the gland to expand and lock into the female's vagina, creating a strong, temporary bond between the two dogs. This natural mechanism ensures effective mating and fertilization.