 animal cells, these chicken cells again and again, what you're doing is you're essentially, you're weakening the effect of the virus on a human. It's still a virus and it's still a virus that you can actually then take and put inside of a human. The thing is, it's just not going to cause the same sort of disease that it would if it were like really virulent and very strong. It's essentially weakened. This is called attenuation. You're kind of like turning down the knob or something, the volume on this virus as you pass it through a chicken.