Researchers often use the technique of RNA interference to identify genes involved in particular biological processes by knocking them down, one at a time, and observing the result. But this approach fails to capture some key players because many genes are redundant. Thus, cells can mask their distress when they lose a single gene by turning to fail-safes with the same function. A team has now overcome this obstacle, using RNAi to systematically knock down pairs of genes in fruit fly cells.