One thing is clear: peering inside animals leads to scientific discovery. In the 1960s and 1970s genetic and developmental biology research exploded after laboratories began studying naturally transparent critters, such as the nematode Caenorhabditis elegans and the zebra fish Danio rerio. With them, scientists could watch young cells develop into a full organism. Now, for the first time, they can see through mammalian bodies, thanks to a technique that can make mice and rats— and perhaps larger animals—clear.

Scientists have been able to render tissues such as the mammal brain transparent, but the procedure can take months. To speed up the process and apply it on a larger scale, Viviana Gradinaru, a neuroscientist at the California Institute of Technology, exploited a rodent’s blood vessels. Using a dead rat, the team pumped a series of chemicals through its vessels and into its tissues. The compounds removed cloudy fats and replaced them with clear liquids. In just two weeks the entire rat turned into a see-through, jellylike specimen. The researchers published their results (including photographs, if you’re not about to eat) in August in Cell.

Postclearing, Gradinaru can look at cells that have been tagged with antibodies or dyes. That ability could help others map nerve fibers or follow cancer cells. “We can see things that we couldn’t before,” says Guangping Gao, a gene therapist at the University of Massachusetts Medical School, who wants to track viruses in the body. Gradinaru says the technique could be scaled to any organism with vasculature—even humans.