Snails don't have really good vision, either, so they miss their target half the time. Then it's not like they can shoot another, because it can take a week to make a new one lol...
Apparently, if they can 'impale' their target, it means there's more chances that babies will happen because the dart is coated in mucus (lovely) full of allomone (a pheromone-type compound).
@rek slimy little cupids :]