Key theory

[nightshade]

I have a theory about why the monks made Dawn the key instead of some random object.

It's her blood that is the key, and blood is constantly moving within the body, so maybe Glory couldn't see it because of the constant movement, despite it only going around the body. If the key was still in an object she may have been able to see it.

That means they could have put it in an animal, but with Buffy at college she perhaps wouldn't have been as good a caretaker as a sister.

 

[Octavia]

Oh gosh, Buffy with a pet would be terrible! ANY of the scoobies with a pet would be terrible. Plus, a gold fish or kitten are not worth risking the fate of the world for.

I like the blood moving theory, its similar to the nature of water. Water is life according to the bible, blood is life according to the demons. Humans are only 'remembered' after the water/life force stops. Dawns skin could also provide a barrier against Glory's senses, because human skin is designed unlike animal skin. Dawn was made from Buffy, possibly another source of protection - the sisters are similar so Dawn does not stand out when close to Buffy. And her family and Buffy has that little bit extra natural care for Dawns welfare.

Tara and other brain damaged can see Dawn for what she is because some senses were stripped raw in the brain suck, so they are more sensitive to the differences in energy.

 

[Ethan Reigns]

In "The Gift", we get this exchange early on between Spike and Xander:

XANDER
Why blood? Why is it Dawn's blood,
why couldn't it be, like, a lymph ritual?

SPIKE
'Cause it's always gotta be blood.

XANDER
We're not actually discussing dinner
right now.

SPIKE
Blood is life, lackbrain. Why do you think
we eat it? It's what keeps you going, makes
you warm, makes you hard, makes you
other than dead. 'Course it's her blood.

This is similar to the explanation of the kosher killing laws for animals given in the Bible:

Leviticus 17:11 For the life of a creature is in the blood, and I have given it to you to make atonement for yourselves on the altar; it is the blood that makes atonement for one’s life.

Leviticus 17:14 because the life of every creature is its blood. That is why I have said to the Israelites, “You must not eat the blood of any creature, because the life of every creature is its blood; anyone who eats it must be cut off.”

Deuteronomy 12:23 But be sure you do not eat the blood, because the blood is the life, and you must not eat the life with the meat.

Judaism as practiced in the Old Testament had a number of rituals involving animal sacrifices where the blood was either splashed against the side of the altar or placed on the horns of the altar or anointed on the right ear lobe, right thumb and right big toe of a person for various reasons. The message about blood sacrifice is that it is Biblical and it has also been adopted by various cults as a means of concentrating power into people. It stands to reason that the Key must be a living thing.