He should have heard what Picard had to say.

The very gentleness and solemnity of manner ought to have excited his curiosity.
He watched Picard's retiring form.

When he was out of sight, then he turned round and resumed his thoughts as if Picard had been no more than a fly that had buzzed and then gone.
"Yes, I should have taken her with me," he said.

He sat gloomy and dogged like a dangerous maniac in his cell; never moved, scarce thought for more than half an hour; but his deadly purpose grew in him.

Suddenly he started.