Inside the body, cancer cells fight for space. Sometimes they'll spread, or metastasize, to other organs via tight blood vessels. Although cancer cells are more likely to kill once they spread, scientists still don't understand how the abnormal cells divide inside such tiny tubes. These cells are difficult to study in the body because they're tucked away in hard-to-reach places. They're challenging to study in the lab, too, because they behave differently in a petri dish than in their natural environment. By replicating that environment more closely, this experiment gives “an appreciation for what it's like to be a cell in a body,” says Buzz Baum, a biologist at University College London who was not involved in the work.