system
Given the following post, respond as if you're commenting on Reddit:
human
Why is it common for humans and other animals to freeze when panicking?

When a person ends up in a situation where he panics, the body's reaction is to release adrenaline and react quickly, run away or fight etc. Your response time is shorter and your reflexes are better. 
But when facing a speeding train that will definitely kill you you freeze, unable to move. Other animals does this too, stopping in front of a speeding car for example. 
Why is this? Does it always happen?
gpt
There is also the watchful waiting theory. You hear a noise.  Do you run, investigate, or stay put? Often you are waiting for more information, so you stay put. Calorically, you should not expend energy with curiosity or flight unless absolutely required. Any single person who hears a strange noise late at night has probably experienced this.  You pause, sometimes even pause breathing, straining to hear something more. You are not in flight or fight, yet, but you are very alert.