User blog comment:FairyRaven/Fairy Tail Chapter 363: The Stories That Demons Read, Review and Commentary/@comment-1153699-20131207173113/@comment-24066070-20131212002424

If you look at it like that, I can also eat a car engine, since it would be possible if I just cut it in small enough pieces. He got sick from eating it and didn't get a powerboost. Maybe, as you said, his power weren't mature enough, but he just shouldn't be able to eat other element. Where would the line be if he can? Fire Lightning Sky Poison Holy Shadow Steel Dragon Slayer? I thought that was the initial concept of Dragon Slayers, they can eat their own element but not alien elements.