However, these patterns are frequently influenced by the surface material’s interaction with the blood itself, particularly when that material is clothing made from cotton. To study these and other attributes, Fang and colleagues used pig’s blood treated to behave consistently across testing. They then lined up five cotton fabrics—plain-woven cotton, the front and back of cotton twill, as well as the front and back of a jersey knit. “We found that the more fingers a bloodstain has, the faster the blood was moving when it struck the fabric,” said Fang. These are created when fast-travelling blood strikes the fabric, creating secondary stains around the central mark.