Which part is the cue
Answer it in your head first, then look.
Someone tells you the way they know they are angry is that they have already raised their voice. What has gone wrong with that as an early warning?
By the time the voice is up, the response has already been chosen and the moment where anything could have been done is behind them. An early warning has to arrive before the behaviour, which means it has to be something in the body. The voice is the outcome, not the signal.