The Garden Snail
Snails are hermaphrodites, meaning they have both male and female sexual organs, but they do not self-fertilize.
Before two snails mate, they shoot "love darts" made of calcium at each other. People used to think that these sharp darts are nutritional gifts, like you give someone you love a box of chocolate.
Scientists now think, however, that these darts serve a more sinister purpose. The mucus on the darts allow more sperms to be stored in the snail’s uterus (and thus helped it gain an edge in reproduction).
There’s no advantage to the target snail (getting hit may even be dangerous as snails are really, really bad shots). Indeed, snails jostle each other not only to get into a better position to fire their darts, but also to avoid getting hit themselves!