The mongols would drink blood from their horses while they were fighting.? There is about 15 gallons of blood in a horse.? A unicorn of similar size should have about the same amount.?

The human body can hold about 2 to 2.5 gallons of liquid before drowning in excess.? It can also not hold that amount of protein without reacting negatively.? This is why no one can drink an entire gallon of milk at once.?

So why do I keep reading about Quirrell draining a unicorn of all it's blood?? It shouldn't be possible.? And the amount that he could possible drink shouldn't have killed the unicorn.?

Now I believe he killed the unicorn before starting to drink from it.? But I also think he should have brought something to hold the excess, maybe.? It just bugs me that it is so unclear.?