* The male dog's penis doesn't actually swell. It's not like a human erection, where the penis becomes larger and harder. Instead, there's a locking mechanism called a tie.
* The tie occurs when the male dog's penis swells inside the female dog's vagina. This swelling isn't a physical change in size, but rather a change in the shape and structure of the penis. It's not visible from the outside.
* The tie can last anywhere from 5 minutes to an hour. This is meant to ensure the sperm has time to reach the eggs.
It's important to note: This is a natural and healthy process for dogs, and it's not something to be concerned about. If you have any questions or concerns about your dog's mating behavior, please consult with a veterinarian.