Here's why:
* Gestation: Dogs have a gestation period of about 58-67 days. During this time, multiple fertilized eggs develop in the uterus.
* Birth process: The birthing process, called whelping, involves multiple puppies being born in succession.
* Litter size: The size of a litter can vary greatly depending on the breed and individual dog. Some breeds have very small litters (like Chihuahuas), while others have large litters (like Labradors).
So, while it may seem like a dog is having puppies one at a time, they are actually all born within a relatively short period.