"A soundproofing spell. As Rainbow Dash mentioned, she cannot be seen... so we are taking precautions." Luna's eyes opened as the light of her horn went out, the aura solidifying along the walls, ceiling and floor. Spike raised his brow at the quick casting of the complex spell; he'd heard talk of spells that could harden the atmosphere itself, but they were usually extremely complex and difficult to cast. Not only that, but they also required monstrous amounts of mana to use, more than most unicorns had in their entire lifetimes.