"Well my dear, in a recent adventure we found an area in a forest that seemed to hurt us, since all ponies have magic in them, forcing us down, creating a painful sensation, and well, not allowing the use of magic."
"Aaaah, dead magic zone. And I take it it's been there for a long while, which is why you're here instead of waiting a few minutes for it to go away...Hmm....Roughly how big would you say it was? A couple feet? A couple dozen feet? A couple miles?"