I used to catch crayfish (though we called them crawdads) in No. Cal many moons ago. I know some use the string and bait (they would grab on and not let go, well at least sometimes) but my friend and I would just reach in and pick them up out of the water.
Because they propel themselves backwards using their tail, you adjust to anticipate it. No I never was "pinched" when catching them.

We would bring them home to my friend's house, where he had a child's pool (no longer used) and they would live in the pool until ready for dinner! (Sometimes we would end up catching 35-40 before they would eat them, but that would be only a couple days of "hunting"!)