Biological “detectives” are tracking down biothreats such as the bacteria that causes tularemia (“rabbit fever”), but they constantly face the challenge of avoiding false positives. Sounding the alarm over a bioattack, only to find it’s a harmless relative in the same genus, reduces credibility and public trust. New work is narrowing down the confusion over Francisella bacteria, a few species of which include highly virulent human and animal pathogens, fish pathogens, opportunistic human pathogens, tick endosymbionts, and free-living isolates inhabiting brackish water.