In reply to Euan Semple.

Wow, that's quite the quote from Melissa.
"A rat who is working for food suddenly hears a warning signal followed by a shock he can do nothing to avoid. After it stops, he goes back to working for food. But soon, even the sound of the signal is enough to stop him from seeking reward. Even though he could continue painlessly during this interval to obtain food, he seems crushed by the anticipation and now “crouches tensely, trembling, defecating, urinating, hair standing on end.” The animal is, in scientific terms, scared shitless. He can do nothing to control his fate, and that is untenable."