 A snail does not have a dart to fire the very first time it mates , because the first mating is necessary to trigger the process of dart formation . Once a snail has mated , it fires a dart before some , but not all , subsequent matings . A snail often mates without having a dart to use , because it takes time to create a replacement dart . In the case of the garden snail Cornu aspersum , it takes a week for a new dart to form . 
