@Karikko They don't, certain animals will consume grass and similar things to deal with stomach problems (like dogs), but overall most carnivores only eat meat. To the point that some of them like the Komodo Dragon (which is fine eating rotting bones) will not eat the stomach of its' prey because it had leaf matter inside of it.
It depends, though.
Even big cats occaisionally embrace
h e r b i v o r e
and munch on grass. Jaguars, in particular, have been observed doing this in the wild in more recent times.
A behavior big cats had adapted to receive nature's laxative that helps expel things in their food like fur, bones, and feathers that don't really digest. There's also the theory that it helps with excreting parasites in their system.
Pretty interesting. Never thought "obligate carnivores" could even digest a plant to any useful extent. I guess there's also those videos of deer and cattle demonstrating that, despite having stomachs strictly designed for plants, they occasionally eat small dead animals on the ground that they can somehow digest to an extent.