        “That’s what it means.  Because illusion spells aren’t always used on cooperating ponies.  They can be used for a magical defense as well.  Did you know that Starswirl first proposed using them thus during the Ponic Wars?  When the Princess’ compound was in danger of being overrun, Starswirl made an illusory—” Twilight’s voice trailed off as she noticed that Rarity’s eyes were glazing over..  “Come on, let’s practice.  See who can fool Spike with a fake gem.”