system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is it that makes carnivores only able to eat meat?
gpt
Carnivores have a really short digestive system that's well-suited for getting nutrients out of meat. 

It takes a lot longer to get nutrients out of fruits and vegetables, which is why we have a much, much longer digestive system. 

Animals like cows have incredibly complex digestive systems consisting of several stomachs so they can get all they can out of *grass*. Pure carnivores have none of that.