In a little-noticed decision in Salinas v. Texas (2013), the Supreme Court just ruled that your right to remain silent to avoid self-incrimination can be voided by your body language. If it seems “suspicious” and you don’t explicitly declare that you’re invoking the 5th amendment, then your unconscious body language during interrogation or questioning can be used against you in court.
A very good observation from the comments at The Volokh Conspiracy:
The problem is that in the eyes of the police and prosecutors almost anything the defendant–the person they believe is guilty–says and does after the crime and during interrogation becomes evidence of guilt, even opposite reactions by different defendants. He was silent; he wouldn’t stop talking. He went out and got drunk with friends (he partied) after the murder; he showed no emotions and took off away from everyone after the murder. He appeared very nervous; he seemed to be very in control of himself. He appeared to be crying but shed no tears; he was shedding tears but a few minutes later he was smiling. It’s a fool’s game.