They need something to believe in since religion isn't the in thing anymore
Huhuhu, very funny richardhead. Cut the "coolbro" irreligious bullstuff, this about the discussion of the possible existence of Dragons, not whether or not we believe in God.
Back on topic,(How this could be if Ike would shut the Hell up and be "compassionate and patient") like the bombardier beetle posted by Tesla, there would be two reactant liquids that ignite when they mix. Two separate glands contain them, and the Dragon would be able to breath flames for a short time before the reservoirs run out of the chemicals. I don't know exactly how long the fire breath could be maintained or how long it would take for the compounds to refill, but it's definitely real.