What does a crayfish do when you touch its back?

I don't know too much about Crayfishes but here's my guess: flips its tail and runs away

Why do I think that? I read this:

When confronted with threatening stimuli and predators, the crayfish responds with an innate escape machanism called the startle reflex. Also known as tailflipping, this stereotyped behaviour involves rapid flexions of the abdominal muscles which produce powerful swimming strokes that thrust the small crustacean through the water and away from danger.

http://scienceblogs.com/neurophilosophy/2008/10/the_staggering_escape_of_the_crayfish.php

And listened to this:

http://www.sciencenetlinks.com/sci_update.php?DocID=69

But I've never touched a crayfish, so I don't really know.