It's ... honestly I haven't done extensive studies on flerken biology because one, Goose is one of the friendlier examples of the species and they don't normally like making friends, and two, they're fairly rare as a rule.

[Speaking of, said flerken hears a familiar voice and hops up onto Carol's shoulder to get a better look.]

Now, does Goose eat people that she does not spit up? Yes. But do the people she does spit up show any signs of acid damage that would indicate you're being held in a stomach or something? No. Everything she's spit up has remained intact.