[ Yes but it's not something you teach an elementary school class. Unless you're Harry Morgan. What did your father teach you, Loki? ]

It lets us compare samples against others for DNA matches, find out if the people are on our database, or in some cases if they have family members who are. In some cases we can even pick them up because they're suffering from a rare disease, or if they have a rare blood type, because it's all right there.

Blood's like a signature left behind at a crime scene. Not as straightforward as a fingerprint, but just as unique.