observed in animals
when they are faced with an unfamiliar, stressful
situation, or one with conflicting drives. What happens is that the creature
reverts to performing some inappropriate
action given the circumstances.
For example, a mouse is cornered by a snake. The mouse doesn't know what to do ... can try running, can try attacking, not sure, probably going to die anyway. So what does the mouse do? It preens itself.
Another example: You have to get that assignment out by tomorrow morning, but you really hate working on it. So what do you do? You decide that night is the perfect time to clean up your room and vacuum the entire building.