User blog comment:Miskos3/Fairy Tail 531: Pegasus vs. Black Dragon/@comment-7418318-20170414215900/@comment-25111584-20170415121118

Meh, Acno getting motion sick in his Dragon Form is completely inconsistent with Irene's explanation, but Irene's explanation itself was inconsistent considering Natsu had no problems being carried by Happy. Mashima should have kept it as Natsu's quirk. e_e