[ This is a topic she can get behind. Simon asking for factual explanations -- or at least implicitly asking for them -- is safe and familiar, and does not touch on scary or horrifying events in their past. ]

I have a theory that they pulled what we look like from our own memories and perception of ourselves, [ she replies, in the same plain, straightforward tone she explains everything with. ] They obviously couldn't have -- [ a short, hitching pause before Catherine pushes relentlessly forward ] -- um, used my actual body. Or yours.

If you think of yourself as missing an arm, then that's what you got.