they grab and shake them, also have been told they have a resistance to the poison, not a biologist so don't know...but if you have sounders of hogs you will have few snakes.
Our dog at work is quite efficient at snake killing. He does like Frank says, grabs the sucker in the middle and shakes so violently that it pops apart. I've been splattered with snake juice a couple of times.
Snakes really do stay clear of hog pens. I have two pot-bellied pigs that have never tasted a snake they didn't like. I don't let Lucy and Ethel out in the yard, so I still have to keep an eye out. My two girls live better than I do some weeks!