Passive Bloodstains
Passive bloodstains are bloodstains formed when gravity is the only external force acting on the bloodstain. Passive bloodstains include drops, drips, clots and pools.
Drops
Blood falls in sphere shaped droplets. The sphere shape breaks when the blood droplet hits a surface. If a droplet falls straight down and hits a flat surface, the appearance of the resulting stain will depend on the surface. A smooth, non-porous surface will result in a circular bloodstain with smooth edges. A rough, textured surface will result in a circular bloodstain with spines extending along the edges.
If a drop hits a surface that is not perpendicular to the blood source, the bloodstains that result will be oval in appearance. As the angle changes and the surface becomes more parallel to the blood source, the oval shape will elongate. The most narrow side of the bloodstain indicates the direction the blood was traveling when it hit the surface.
Blood into Blood
This is a pattern that is created when blood drips into a pool of blood. This pattern can be identified when a secondary set of smaller spatters is seen around the periphery of of the primary blood pool.
Clots
A clot is a mass of congealed blood. Clots often show a separation of the solid (cellular components) and liquid (serum) parts of the blood.
Pool/Flow Patterns
This is a pattern that is created when a volume of blood moves across a surface as a result of gravity.
Void
A void is the absence of blood in an otherwise continuous bloodstain pattern.