Is it possible for a fire-breathing creature to exist?
Yes, it should be possible. There is a type of beetle called the bombardier beetle which creates a small chemical explosion to ward off predators. This is created by mixing two volatile chemicals stored in seperate glands. It produces boiling gas which scalds the skin, not exactly fire, but with the same effect. Things like electric eels can also burn predators with an electric shock. Naturally, no animal would evolve to produce fire, since that could ignite the forest and destroy the creature itself! But, aside from that, there is no reason why an animal like could not have fire-producing chemicals.
