Mice have a specialized organ in their noses that picks up chemical signals, called the vomeronasal organ, which helps them detect pheromones emitted by other mice. These mice pheromones have a direct effect on behavior–most obviously in the realms of mating and fighting. In this new study, published in the journal Cell, neurobiologist Lisa Stowers decided to investigate whether the vomeronasal organ was capable of picking up signals from other species as well.
The reseachers took normal lab mice and mutant mice with inactive vomeronasal organs and presented them with cotton balls laced with predator smells, including cat saliva and rat urine. The normal mice backed into the corners of their cages as if trying to escape a predator’s attention, but the mutant mice showed no signs of concern. The mutants were so relaxed that they didn’t even react when a live but anesthetized rat was placed in their cages.
By process of elimination, the scientists were able to isolate some proteins that spelled "cat" to the mice's vomeronasal organs. Link