Dogs get stuck during mating due to a natural, temporary physical phenomenon called a copulatory tie. Here’s what that involves and why it happens:

• What happens physically: During copulation, the male dog's penis contains a bulbous structure at the base (the bulbus glandis) that swells with blood once inside the female. At the same time, the female’s vaginal muscles contract around the swollen glandis. The combination creates a temporary “lock” that keeps the dogs connected for a period of time, typically several minutes to about half an hour. This ensures successful ejaculation and sperm transfer. After the swelling subsides and the muscles relax, the pair can separate. [general canine reproductive anatomy and copulatory tie concepts]
• Why it’s normal: The tie is a natural part of canine reproduction and serves biological purposes, including better chances of fertilization and, in wild settings, reducing the likelihood of another male mating immediately after. It is not a sign of distress or harm when it occurs in healthy dogs. [natural function of the tie]
• How long it lasts: The tie duration can vary but commonly lasts from about 10 to 30 minutes, though shorter or longer instances can occur. It’s important to remain calm and avoid forcing the dogs apart during this time. [typical duration ranges]
• What to do (and what not to do): Do not yank, pull, or attempt to forcibly separate the dogs. If the dogs do not separate on their own within a reasonable time or if there are signs of distress, contact a veterinarian. In most cases, the tie will resolve on its own as the penis and vaginal muscles return to their normal state. [care considerations and when to seek veterinary help]
• Relation to pregnancy: A tie increases the likelihood of successful insemination, but pregnancy can occur with or without a visible tie, depending on many factors including timing and biology. If pregnancy is desired or in questions of breeding, consult a veterinarian or a licensed breeder for guidance. [breeding considerations]

If you’d like, specify whether you’re asking about the biological mechanism, typical duration, care during a mating tie, or breeding considerations, and I can tailor the explanation further. [context clarification]