User blog comment:Miskos3/Fairy Tail Chapter 334: Sin and Sacrifice, Review/@comment-10559926-20130607154927/@comment-7418318-20130607183215

Sometimes they get cuts after being summoned, but as with everything else that is very inconsistant throughout the series.

Sometimes the pop after taken "lethal" wounds, sometimes they pop after a little punch and sometimes they even bleed.