While you have the right to remain silent, I remember reading somewhere that you have to actively invoke that right (by stating something like "I invoke my 5th amendment right to remain silent") for your silence to be considered an invocation of that right, and not merely suspicious behavior, an implicit admission of guilt, or obstruction of justice.

This is actually reprehensible, since invoking a right should mean actually engaging in it (e.g. remaining silent), with no explanation necessary.

Another topic that everybody should know about is juror nullification.