How can I add a comment after a quesition has been resolved?

I tried to add a comment to a resolved question because I saw an area for adding comments, but even though I pressed the SUBMIT box it did not appear to send it? The one about my cats puke everyday---I wanted to convey the possibility of her cats being allergic to red dye in the cat food, and suggest that she try Naturals by Purina in the green bag. What did I do wrong?