Unicorns

A unicorn was a magical creature. The hairs of a unicorn are worth 40 galleons a strand, so they are very valuable. As seen in Harry Potter and the Philosopher's Stone, Lord Voldemort was seen drinking the blood of a unicorn.

Unicorn Blood
The minute the blood touches your lips, you will lead a half life, a cursed life.

-Firenze to Harry

''But who would choose such a life?"

-Harry to Firenze

Can you think of no one?

The blood of a unicorn is a blessed, yet cursed thing. Even, as Firenze said,if you are an inch from death, unicorn blood will sustain you if you have a supply. Lord Voldemort was drinking the blood of a unicorn when Harry Potter and Draco Malfoy were in the Dark Forest with Hagrid.