Everything you need to understand or teach De Natura Unicorni by Jane Yolen.
'"The unicorn,'" Brother Bartholomaeus said, "'is a right cruel beast.'" Brother Bartholomaeus was a real person who wrote about unicorns in the thirteenth century.
Although Yolen regards Brother Bartholomaeus' disquisition on unicorns as "boring," she takes his opening phrase and uses it as her story's opening phrase. Her version of Brother Bartholomaeus turns out to be an extraordinary blowhard who never stops talking, lecturing endlessly about his research into unicorns...