Advances in computational modeling are helping to clarify the behavior of blood under both healthy and unhealthy conditions. Two researchers in particular are modeling blood’s component parts, albeit at slightly different scales. One is trying to describe the molecular mechanisms that drive coagulation, while the other is trying to predict changes in blood viscosity by modeling individual red blood cells and their interactions. Like microscopes that offer different levels of magnification, their simulations illuminate the inner workings of blood at multiple levels.