User blog comment:Omega natsu2/Chapter 397: Steel, Predictions./@comment-125.212.122.46-20140816022634/@comment-4829046-20140816162101

The movie made it so that his organs/innards could be pierced but then Gajeel can just tighten his muscles and break off all the protrusions(also occurred against Yomazu). I assume the broken metal just goes into storage like when he eats. It is kind of a thing to assume that being a Metal Dragon means your body can never be hurt on the inside by metal, or else you would die the moment you use a Roar or anything really. Same way Natsu's insides can never be burned, but sadly people actually getting "burned" in this series is almost nonexistent so Gajeel's example is best. Sting can also be taken as an example, which would mean all the DS have superior muscle and tissue strength.