The transformation from caterpillar to butterfly usually happens quietly, inside a firm opaque husk that protects the pupa as it slowly forms its showy wings.

Back in 2015, at a summer course in Woods Hole, Massachusetts, some graduate students had a relatively simple idea that would enable them to get a closer look into this metamorphosis.

In the lab, graduate students Julian Kimura from Harvard University and Ryan Null from the University of California Berkeley made a small incision into the side of a caterpillar and pulled out the blob of cells that normally form the forewing in a butterfly.

After this surgery, which doesn’t hurt the caterpillar, they let it pupate—but the cells they removed created a clear window