This is also the time when a dog’s penis does something unique.
“A dog’s penis has a bone in it, and in the middle of the bone there is a gland inside it that swells up when the male’s copulating,” “The purpose is to keep the penis inside the female.”
Once that happens, the dogs are stuck together for a short period of time until the swelling goes down. This is often referred to as a male dog “tying” a female.