What can I NOT eat as a vegetarian?

I want to become a vegetarian. If I do, I would be a lacto-ovo-pestician. Meaning, I can eat fish/seafood, milk products and eggs. So, basically, the only thing I can't eat is well, MEAT. I know that. But what i'm asking as a vegetarian, is are there other products that I should be aware of that I can't eat? Like, I know glueten-which is in marshmallows and jell-o- is made from horse hooves. Stuff like that. Please and Thank youuu!!!! :DDD