The gut commensal Segmented Filamentous Bacterium (SFB) is found in a wide range of vertebrates where it undergoes an unusual life-cycle. Unicellular bacteria called intracellular offsprings (IOs) attach to the ileal epithelium, grow out into filaments and then divide and differentiate to produce new IOs that are released from the filament end. In a publication in January 2020 in the journal Nature Microbiology, the Lab or Host-Microbiota Interaction directed by, Pamela Schnupf discovered that half of the tear-drop shaped IOs released from their mother filament are flagellated. Flagella are appendages that permit bacterial movement and, together with the ability to sense chemoattractants, enable the bacterium to reach its replicative niche. The team also showed that the major structural component of this appendage can be sensed by the host’s innate immune system. These findings add a missing link of immunological importance to the life-cycle of SFB, a potentially medically-relevant commensal.