This experiment is designed to demonstrate that blood like all liquids will travel in the path which offers the least resistance. There are of course various factors which should be addressed, such as the volume of blood present, the surface the blood is on as well as the effects of gravity and adhesion.
Notice in the picture to the left the direction(s) that the blood decides to travel;
it is taking the least path of resistance on this vertical surface. This was a path created by the release of a few drops of blood. What would the path look like if the volume of blood was greater or on a smooth surface? This is why it is essential to take into effect all factors; not just the ones listed above but temperature and humidity as well.
This stain was created by placing blood on a flat poster board and then spraying it
with a can of compressed air.