[Watch the scene from "Part I" above and see the full episode here.]
We don't see much of Cora (Jessica Biel) as a mother in the moments preceding her crime at the beach, but what we do see is someone who's struggling. Biel gives her take on what kind of mom Cora is to her young son and the hints shown in the first episode of The Sinner.
During one moment early in "Part I," Cora looks over her friend Heather who's fawning over her own child, which then prompts Cora to act similarly toward her son. We asked Biel what Cora was thinking in that moment.
"Cora feels insecure as mother; she doesn't quite know who she is as a person," Biel told USA Network. "So I think when you're in that kind of place in your life and in your head, and you have a child, you struggle. She's struggling with, 'How is that woman [Heather] doing that so naturally? Should I be doing that? Am I doing it wrong? Is she better than me?' There's a real sense of unease about how she behaves with her child, because she's not comfortable with who she is. That's why we did that."
So, where does that feeling of insecurity come from? The Sinner director Antonio Campos elaborated.
"Cora is a new mother and she's a good mother," Campos explained, "but there's still a disconnect that's in that character that we start to understand based on her own childhood and some of the things that have happened to her over the years. There's a sense of 'Am I doing this right? Am I behaving like the normal housewife should?' She's taking stock of how other people behave."
Biel agreed that Cora does not necessarily intuit how she's supposed to behave toward her child, and watching Heather do it so naturally creates a feeling of guilt within the young mother.
"That was kind of shameful and guilty, like "I'm not taking care of him," Biel added. "'Oh, I should have touched him. I should have caressed him more -- you know, loved him,' and she just doesn't do that naturally."
As Campos alluded to -- and as you see in "Part I" of The Sinner -- Cora's own childhood will fill in some of these questions and more.