Blood

“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.”

―Spike^[src]

Blood was a bodily fluid found in most beings, including humans and demons. Aside from its basic biological functions, blood was known for its numerous mystical properties, making it a key ingredient in many magical spells and rituals as well as a source of food, in special for vampires.

Properties

Consumption

Drusilla blood — Drusilla drinks a person's blood.

Vampires were well known to feed on the blood of mammals, in special of humans, but also from rats and pigs.
In order to make a new vampire, the sire would have to drink a large amount of the victim's blood before letting the victim drink some of theirs.
Sebassis kept his slave of the same species, whose blood was regularly extracted from his body and made into a refreshment for his master.^[1]^[2]
The consumption of blood could provide details about the person. Glorificus instantly determined that Tara Maclay wasn't the Key by licking her bloody hand^[3] and Spike confirmed that Cordelia Chase wasn't a demon after drinking some of her blood.^[4]

Curative/healing

Blood of Eternity — The blood of a Mohra demon.

Mohra demon's blood, known as Blood of Eternity, possessed potent healing properties and was even able to revert a vampire back into a human.^[5] During the end of magic, it kept on regenerating the cells and developed a kind of cancer.^[6]
The blood of the Slayer was the only known cure for the Killer of the Dead, a poison specifically designed to kill vampires.^[7]^[8]

Power granting

The blood of an unidentified telepath demons could grant telepathic abilities to whoever made contact with it.^[9]

Telepath Demon blood — The blood of a telepath demon.

Slayer's blood could strengthen vampires. This was most evident when the Master used Buffy's blood to break free from his prison.^[10]
The power of the Senior Partners was granted to Marcus Hamilton within his blood. Drinking his blood granted the consumer with his power.^[2]
Consuming blood from prophetic demons, such as Splenden beasts, could give vampires visions.^[11]

Uses in magic

The vampire restoration ritual involved using the sire's blood to restore a vampire's strenght.^[12]
Blood was a central ingredient in resurrection spells,^[13] such as the enchanted Vino de Madre.^[14]
Blood was needed to open the Seal of Danzalthar.^[15]^[16]^[17]^[18]

Sunnydale Seal of Danthazar — Jonathan's blood pouring over the Seal of Danzalthar.

Angel's blood was the key ingredient in the ritual of awaken Acathla as only his blood-soaked hand could remove the Sword of Virtuous Knight from the demon. Likewise, his blood was needed to stain the blade of the Blessed Sword used to deactivate Acathla.^[19]
As the human form of the Key, Dawn Summers' blood possessed the power to tear down the barriers between Earth and other dimensions when used in the proper ritual. Since Buffy shared the same blood as her, she was able to close barriers.^[20] Buffy's blood was also a key ingredient to restore Dawn after her disappearance from lack of magic.^[21]
An unidentified shaman needed Darla's blood in order to identify her unborn child by mixing the blood with other ingredients and touching her stomach with the blood on his hands.^[22]
The blood of any demon was required to open a portal to Beljoxa's Eye dimension.^[23]
The Cloaking Dissolution Spell required arterial demon blood.^[4]
Flesh Magic was a kind of magic based on the employment of flesh and blood to perform spells and rituals.^[24]^[25]
Spilling blood on the Mark of Gachnar would summon the fear demon Gachnar.^[26]

Color

Blood could come in various colors depending on species.

Red: human, vampire.
Black: Bezoar, Ancient Mummy Hand, Turok-Han.
Blue: Ghora demon, Doc, Skench demon, Jenoff, Sebassis's species, Yastigilian hound.
Green: unidentified demon, Mohra demon, Fyarl demon, Spawn of Sobek, Durslar beast, Baby-killer demon, the Swell, Plagiarus demon.
Purple: unidentified bug demon, demon broad.
Yellow: Skilosh demon, Kungai demon, Wig Lady, parasite demon, root monster, Suvolte demon, Spike's crew.
White: unidentified telepath demons, Glarghk Guhl Kashmas'nik.

Additional properties

According to Spike, blood smelled metallic, similar to a penny.^[27]
According to Spike, demon's blood tasted astringent and oaky.^[4]
Spike noted as well that the blood of an unidentified demon tasted like Vegemite.^[28]
Slayer's blood was said to be a great aphrodisiac.^[29]
Eating the Doublemeat Palace's Doublemeat Medley made the consumer's blood undesirable to vampires.^[30]
Drinking/smelling blood could free the consumer from forms of mind control.^[31]^[32]

Behind the scenes

In the non-canonical Buffy the Vampire Slayer 2002 video game, a pair of vampires were seen discussing whether they should eat out at a drive-through because one of the vampires claimed that the blood of fast-food clerks tasted delicious, while the other vampire considered them too greasy because their high cholesterol gave him gas as a result.

References

[1] "Power Play"

[NFA-2] 2.0 ^2.1 "Not Fade Away"

[3] "Tough Love"

[YW-4] 4.0 ^4.1 ^4.2 "You're Welcome"

[5] "I Will Remember You"

[6] Live Through This, Part Four

[7] "Graduation Day, Part One"

[8] "Graduation Day, Part Two"

[9] "Earshot"

[10] "Prophecy Girl"

[11] Angel: After The Fall

[12] "What's My Line? Part Two"

[13] "Forever"

[14] "Bargaining, Part One"

[15] "Conversations with Dead People"

[16] "Never Leave Me"

[17] "First Date"

[18] "Chosen"

[19] "Becoming, Part Two"

[20] "The Gift"

[21] The Core, Part Five

[22] "That Vision-Thing"

[23] "Showtime"

[24] "Sacrifice"

[25] "Peace Out"

[26] "Fear, Itself"

[27] "Damage"

[28] Spike: Into the Light

[29] "Fool for Love

[30] "Doublemeat Palace"

[31] "Buffy vs. Dracula"

[32] "Sleeper"

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