I noticed the snail's carapace looks like a question mark. Perhaps that says it all. In terms of the joke, there isn't one. I picked him up and placed him in the woods where the likelihood of getting flattened by a car is pretty remote.
I must confess- being a Catholic- that my idea of organic pest control used to be flinging the snails and slugs into my neighbour's garden. I won't be a hypocrite and say I was particularly sorry or remorseful for doing this. I'll just settle into the sofa now and wait for the fire and brimstone.