The Magic of the Unicorn

From the back cover: You Must Seek The Realm Of The Unicorn Only a unicorn's horn can purify the water in your medieval village - so you set off to find a unicorn. After a long search you meet a sorceress who promises to help you. She offers you a choice of two spells. Once will give you the power to speak with animals. The other will weave you a golden net for catching magical beasts. Which spell should you choose?