"And be sure to tend to the magic harvest every other day. The unicorns really dislike being held in large pits, so you must satiate them with large vats of oil."
"What."
Tirek pat Cozy on the back, almost crushing her by accident. "It is part of the learning process, dear child. Soon enough, you'll be an evil power-hungry tyrant like me, and then you'll need to find a source for your own nigh-infinite supply of magic!"
Unfortunately, the centaur had never specified what kind of oil was to be used and so once the unicorns were covered in oil and it began to rain they proceeded to fly out and escape from the pits.
Oops.