Theory: Saul and Mama Are immune?
I find it interesting that Saul can breath at ground zero, where I suspect you can get converted if unprotected, and Mama didn't turn (and I don't think she will)... Obviously an inherited immunity.
Natural Resistance to Zombies
Is it just me, or does Saul & his Mom have a natural resistance? Thinking of the close calls Saul has had, his reaction to ground zero, and his mom's wound... something is there that makes others think she should turn... Not everyone seems so resiliant.