Only one who has nothing to lose, and everything to gain, would commit such a crime. The blood of a unicorn will keep you alive, even if you are an inch from death, but at a terrible price. You have slain something pure and defenseless to save yourself, and you will have but a half-life, a cursed life, from the moment the blood touches your lips. Firenze the Centaur So brightly white it makes snow look gray. Unicorn hoofs are golden.
Unicorns prefer a woman's touch.
Unicorn foals are pure gold. They turn silver when they're about two years old. They grow horns at around four. At about seven years old, they're fully grown and turn pure white. Interestingly, the two people who we know have unicorn hairs in their wands are Cedric Diggory and Ron Weasley.