You’re alone in your house, and something just woke you up in the middle of the night.
There is a long period of silence.
Then you hear someone start to whistle, and then footsteps, slowly heading for your bedroom.
It’s an adaptive response we share with other creatures, and it prepares us for danger.
Adrenaline is released, heart rate increases, blood flows into the muscles, the digestive system shuts down and consciousness narrows, focusing on the threat.