Scientists in the U.S. have made biological tissues of live mice transparent using a solution of the dye tartrazine, which absorbs light. The dye was applied to the shaved scalp of the mouse, allowing researchers to visualize brain blood vessels with laser speckle contrast imaging. The solution also made the mouse's abdomen transparent, enabling direct observation of internal organs like the liver, intestines, and bladder. Remarkably, the effect is reversible by simply washing off the solution with water.