depends on the animal…crocodiles and other reptiles have very strong stomach acids…they tend to digest a lot longer as well…they also eat stones to help grind up the tough bits…a large meal can last a whole year…mammals need bacteria to aide their digestion…they also ingest fur along with a meal..in small amounts it acts as fiber…meat eaters have gut flora and fauna made to do the job…many mammal predators also consume plant material…dogs do it to vomit something that upsets their stomachs…bones are not always digested totally,and the trowing up is helpful to them…i have seen dogs eat tomato plants,which are poisonous,just to evacuate their tummies…canines will also eat charcoal on occasion to soak up harmful materials…

snakes also use venom to dissolve their prey…many of the tissue destroying venom’s will literally liquefy meat,bone,and most other tissue..venom is related to saliva,which on its own serves to soften food…

The meat eaters generally have short, straight intestines. The whales and other marine mammals have long intestines, ostensibly to extract water from the food.

"Under normal circumstances, the colon gradually removes the remaining water, and forms a shaped stool, which moves toward the rectum as a result of gentle pressure waves. In people who eat too little of fiber-containing foods, the stool becomes hard, dry and small. Whereas the soft, bulky stool can move easily along the passage of the colon, the hard, dry stool sticks to the dry wall of the colon and requires that the colon develop high-pressure waves to be moved. Years pass, and the colon is no longer capable of generating such high pressure waves. The colon now requires assistance to push along the hard, dry stool, and the abdominal muscles begin to contribute the necessary force."

As you can see, people have problem with constipation because we have long, winding intestines that require "waves" to move the stool. Short, straight intestines most carnivores have can move hard dry stool more easily.