Mrs Birling really puts her foot in it
1. While Sybil is blaming the father of the child, the Inspector doesn't intervene, but instead lets her walk straight into a trap - demanding that he punish her own son
2. This is the most dramatic result of questioning each person separately - Sybil answers the Inspector's questions, totally unaware of what Eric is going to say
3. But Sheila is open to the idea that her family are guilty and guesses that Eric might well be the "young man" that Sybil's determined to blame