1. A method of characterizing the coagulation or sedimentation dynamics of a fluid such as whole blood, a blood fraction, or blood plasma, the method comprising: illuminating a sample of said fluid with a beam of coherent light; acquiring a time series of images of a speckle pattern generated by interaction between said sample and said spatially coherent light beam; and processing said time series of images; wherein said processing step includes calculating a function representative of the variation in said speckle pattern between two or more images of the series.