Trichomonas vaginalis is a small anerobic, parabasalid protozoan that moves with the aid of four whip-like flagella that protrude from its front end. It also has a fifth flagellum extending rearward from an undulating membrane that allows the parasite to attach to and tear the urethra or vaginal walls, causing inflammation that aids in speeding and intensifying infection. The adults (called trophozoites) then live in the urinary or reproductive tracts, until they are passed onto their next human host though unprotected sex.