This video shows the rapid "twinkling" or intensity fluctuations of the speckle pattern in a drop of unclotted whole blood. The rapid "twinkling" is due to the fast thermally-driven motion of blood cells that scatter light.
(Photo Credit: Seemantini Nadkarni)
This video is taken from the same sample of blood featured in the Speckle Pattern in Unclotted Whole Blood video after 10 minutes. In this case, the time-varying fluctuations of the speckle pattern are markedly reduced due to the restricted motion of the blood cells that aggregate or are trapped within the clot. By quantifying the fluctuations of speckle patterns, researchers can measure changes in clot stiffness rapidly and with exquisite measurement sensitivity, using just a drop or two of whole blood.
(Photo Credit: Seemantini Nadkarni)
Source: The Optical Society