User blog comment:FairyRaven/Fairy Tail Chapter 329: Seven Dragons, Review and Commentary/@comment-4829046-20130430111358/@comment-203.87.139.100-20130430123042

maybe Natsu is just like giving a clue to F.Rogue on "who's the 7th DS?"

How Natsu knows? Strong Smelling sensation. possible ultear tells jellal's plans.. :)

Or maybe, natsu's hearing sense is improve as evidence in Lucy's fight with Flare