Hello, I'm Dr. Kara. I have over 20 years of experience as a veterinarian and I'd like to help with your concerns about Bob Marley and his eating Zinnia plants.
Zinnias are not a toxic plant for dogs, so that is good news.
Dogs will sometimes eat plants though when they have an upset stomach. If they eat enough plant material they will vomit, and if they vomit a lot or eat large chunks of plant material they can irritate their esophagus or stomach enough to make it raw and bleed a little, thus the reddish color to his vomit.
I would try to stop him from eating the plants.
To help heal his irritated stomach or esophagus at home you can give either: 1) Pepcid ac (famotidine) at ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 24 hours
These are acid reducers and should help him feel a little more comfortable and heal a bit faster.
I also recommend feeding soft foods mixed with water to make eating and swallowing more comfortable. If he is refusing to eat even soft foods you can try offering a bland diet of 1/3 boiled, shredded white chicken or lean ground beef and 2/3 boiled white rice. You can mix in low salt chicken or beef broth or warm water to make the food softer and easier to eat and swallow.
If he refuses to eat he should see his veterinarian for an examination, intravenous fluids and supportive care.
If he is continually eating plants and vomiting perhaps he has a sensitive stomach and he needs a special diet, like Hills Science Diet food for sensitive stomachs.
Best of luck with your fellow, please let me know if you have any further questions.