User blog comment:Miskos3/Fairy Tail Episode 215: The Snake Charmer Ophiuchus, Review/@comment-4489126-20150110050935/@comment-7418318-20150110103936

But considering how Lucy needed Gemini, trained and still couldn't get it fully right, it's obviously far more involved than just saying the words.

Then there's the problem of hearing them in the first place. Nobody in the audience seemed to hear Flare when she gave Lucy orders and only Natsu's exceptional hearing picked up Lucy shouting "Asuka", so how could Yukino hear the full incantation word for word?

And even if she did, there are only very few people who could learn such a long incantation from just hearing it a single time.