We report on participatory design research where interaction designers, and canine behavioral specialists, together with their cancer detection dogs, teamed up to better support the dogs' life-saving work. We discuss interspecies communication challenges in cancer detection training, requiring the dogs to use human signaling conventions that perturb their detection work. We describe our effort to develop a technology that could resolve those challenges, and how in the process our design focus gradually shifted from a human-centered to a canine-centered interaction model. The resulting interface, based on honest signaling, re-centers cancer detection practices on the dogs themselves, enabling them to better express their potential as cancer detection workers; it also provides a model for re-thinking human-computer interactions.