obligate doesn't mean you can't eat other things, it just means that's the vast majority of the diet. Cats are obligate carnivores but very much enjoy eating some grass now and then, and when catching things in the wild i assume they'll end up eating the stomach contents of their prey (which will be plant matter).
And of course there's those infamous clips of herbivores casually eating meat, because food is food. (they just won't eat a lot of it, because that would make them sick). It's like how we can eat a couple strands of grass, but if we try to make it a regular part of our diet we'll get constipation.

Well, at least we all know they're very smooth ;)