What does "being silent" mean?

When I first heard about the Supreme Court decision that you have to actively tell police officers you aren't answering questions and invoking your Miranda right, I thought it was ridiculous.

When I read the details of the case, I became less sure.

The suspect in question sat mostly silent for 3 hours while police badgered him with questions. Mostly, I think, is a key word. The man

said little during the interrogation, occasionally answering 'yes,' 'no,' 'I don't know,' nodding his head and making eye contact as his responses. But when one of the officers asked him if he prayed for forgiveness for 'shooting that boy down,' Thompkins said, 'Yes.'

If he answered some questions, even with "yes" and "no", that's not silence.

God forbid I should be interrogated for 3 hours by the police. But if I have a right to be silent, I think actual silence would be what I'd want to provide.

The court's requirement that I say I'm being silent is a little absurd, since I have to contradict myself. But given the case they had, I can understand ruling against the guy who wasn't totally silent.