If you have to kill another creature, can I suggest that you do it as quickly and humanely as possible? Putting salt on a snail causes it to suffer a slow and lingering death. Whether or not it feels pain as we do is unlikely, but I don't see any reason to torture it.

If you are killing snails because they eat your plants, I might point out that salt isn't too good for them either. Try eating them, or exiling them.

For a start, I agree with PB. I don't know whether snails suffer, but people who "prove" that they cannot because of their simpler central nervous system are onto a serious non-sequitur. Generally speaking, it is a helpful rule to assume that if it looks like pain, there might be pain. Anyway, frothing is just about the only defence a snail has apart from retracting into its shell. It puts off some kinds of predators, and washes away some other kinds. It also washes away some kinds of chemical accidents, just as you might well wash salt out of your own eye with tears or water. That also works when it is hurt by crushed, roast eggshell or dry sand and similar things that you would want kept out of your eye. You can work out for yourself that if an irritant such as salt lands on a snail, it would not help for it to retract into its shell. It would do better to stay extended and try to get rid of the problem outside. Does that tell you what you wanted to know? Oh yes! PB also mentined eating the snails. Some kinds are very nasty, but if your snails are Helix aspersa or Helix pomatia, the so-called brown garden snail and edible snail, they are among the best. We tried them when our sons were at school and all agreed that it was good, but not as good as sea food, so we did not bother to do it again. If hunger were a factor though, we should not hesitate to do it again. Cheers,   Jon