The study is flawed. Ever worked as an EMS? On sweaty, grimy, warm skin someone’s blood will run every which way, even in nearly horizontally rivulets. It flows. It gushes. It spurts. It mixes with sweat. I’ve been sprayed with blood from flailing limbs. Put a few drops of blood on your arm and jerk it hard to mimic a spasm. You can never reproduce violent outdoor traumatic blood flow on a body in pain with plastic tubing, air conditioning, calm and shower fresh skin.