Dogs typically engage in mating behavior that is instinctual and driven by biology. The most common position for mating in dogs is called the "tie" or "lock," where the male mounts the female from behind. During this process, the male's penis swells inside the female for a time, which is a natural part of canine reproduction.
It's essential to remember that mating behavior in animals should be viewed through a biological and reproductive lens rather than a sexual one as understood in human terms. Additionally, responsible pet ownership means ensuring that animals are not allowed to mate indiscriminately and that they are spayed or neutered to prevent unwanted litters and health issues. If you have any questions about dog behavior or breeding, it's best to consult with a veterinarian or a professional animal behaviorist.