"An Infestation of Unicorns" is one of many stories Yolen has written about unicorns. The nature of the unicorns varies greatly from one story to the next, with their sometimes being herding creatures, sometimes being solitary creatures, and sometimes being a mixture of solitary males and herding females. In a story such as "The Healing Horn," the idea of unicorns is more important than their actual existence.

"The Healing Horn" has a modern setting in which two brothers and a sister (loosely based on her own children, Yolen says) discover a horn that has been made into a walking stick, along with an advertisement that says the horn will cure many diseases.

There is a foundation in reality: The walking stick and the advertisement are drawn from swindlers of the nineteenth century, and the notion of the horn having healing properties is echoed in medieval folklore...