V. Usually as a result of an infection or disease (from aliens or zombies), when a persons blood becomes volatile and unstable until it violently erupts from the infecteds body.
"Those doctors couldn't help her. She gotbit and they knew she would blood explode"
The blood circle refers to a knife, saw, and axe safety requirement taught primarily in Boy Scouts that must be respected when the user of the knife, saw, or axe is cutting. If the knife, saw, or axe user can turn all the way around in a circle without accidentally cutting someone with the open blade, or sharp object it is safe for the knife, axe, or saw user to operate. To earn your required whittling chip in Boy Scouts that allows you to operate/cut with a knife, saw, or axe you must demonstrate proper knowledge of the blood circle.
One of the first things you are taught in Boy Scouts is establishing the blood circle while using a knife, axe, or saw.