Botox, or onabotulinum toxin type A, is produced by botulinum bacteria. A similar toxin, when consumed orally, can cause botulism which leads to diffuse paralysis and usually kills by inhibiting breathing. When Botox was being developed for human medical use as a treatment for facial spasm, it was tested on a particular European mouse strain. They gave it in small amounts to the mouse until they found a dose that was fatal to half the mice. This dose is the basis for a "unit" of Botox. A fatal dose in humans would be dramatically larger and would have to be given in such a way that it reached the lungs or heart. In cosmetic use, at the small doses we give and in the facial locations, this is very unlikely to occur, though not impossible. Breathing problems have been reported in patients receiving Botox injected into the neck for torticollis, but these injections are of much higher doses and are placed near major blood vessels.