Easy to Swallow
A dog's mouth works differently from a human's. For starters, he has 42 teeth and nearly 2,000 taste buds, while a person typically has 32 teeth and as many as 10,000 taste buds. The reason for this reflects a basic difference between species: While we can take our time and enjoy the taste of a meal, getting as much enjoyment from the flavor as from filling our stomachs, a dog generally cannot. Dogs are designed to find food and eat as quickly as possible. Taste is secondary. Also, a dog's teeth are not capable of grinding like people's do so they often swallow their meal whole. The sole focus of the dog's mouth is to get the food down, through the esophagus and into the stomach as quickly and efficiently as it can.
Hard to Stomach
When people chew food saliva is produced, which contains an enzyme that helps break down food before it gets to the stomach. In dogs, all of the work has to be done in the stomach. The dog's pancreas will begin producing enzymes that will help in breaking down the food; the stomach wall also has glands that produce necessary acids. Since what goes into a dog's stomach can be anything from grass, meat, kibble or bone, the acids must be particularly powerful (in comparison, the acid in a dog's digestion is about three times stronger than in a human's). A dog's stomach will work on breaking down food for roughly eight hours before passing it into the small intestine.
End of the Line
The broken-down food will remain in the small intestine for up to about two days, depending on the meal. Simple food, such as corn, will pass in a matter of a few hours, but bone or more complex material takes quite a bit longer. Whatever remains after the dog's small intestine has done its job, is then processed in a few hours by the large intestine, and moved through the colon. In all, the entire process, from the time a dog bites into his food to the time waste is produced, can take about 10 hours to a couple of days.