The three usual wand cores, used by Ollivander, throughout the series are phoenix feather, dragon heartstring, and unicorn hair. However, its said that other magical substances can be used, such as Fleur Delacours Veela hair. The Elder Wand, in the same vein, contains a Thestral tail hair as its magical core, which is a tricky substance to master, as only somebody who has seen and accepted death can even see it. This is interesting as it ties in with the Master of Death aspect of the Elder Wand, as whosoever possesses it along with the two other Hallows effectively masters death. Also, the Elder Wand has a bloody history, filled with the death of its many masters enough so that it garnered the moniker Deathstick and Thestrals are closely associated with death as well. Another interesting point Rowling made on the Elder Wand is that it is not, like most wands, loyal to an owner: it is unsentimental, giving its allegiance only based on strength.