Four followed after Conall. She didn't feel safe leaving him alone just yet.
"I can see that you're confused. Allow me to explain! You see, this Securitron is running a copy of my neuro-computational matrix, which I guess you could just call my 'brain' if you really wanted to! Anyway, the main copy of my 'brain' is back at the Lucky 38, so if this Securitron gets reduced to non-functioning status like the other one, I can just send out yet another one with another copy of my 'brain'! Isn't that neat?" Yes-Man explained to EMily.