At the surface of every living cell, sugar chains have long been present but poorly understood — until now. Researchers in Japan have discovered that these glycan molecules form fleeting, repeated pairs on cell membranes, lasting only fractions of a second, yet collectively exerting a sustained brake on the growth signals implicated in cancer. It is a reminder that in biology, as in life, it is not the permanence of a connection that determines its power, but the faithfulness of its return.