The oddest thing I learned from Wikipedia recently is that when snails mate, they attempt to shoot one another in the head with a calcium ‘love dart.’ Snails are hermaphroditic, exchanging sperm with one another and later using it to fertilize their own eggs. In Helix aspersa, the darts are coated with chemicals that cause the ducts in the other snail to contract, possibly suppressing the function of sperm-digesting enzymes.
The whole process sounds rather perilous:
The darting can sometimes be so forceful that the dart ends up buried in the internal organs. Sometimes the darts pierce the body or head entirely, and protrude on the other side…
The dart is shot with some variation in force, and with considerable inaccuracy, such that one-third of the darts that are fired in Helix aspersa either fail to penetrate the skin, or miss the target altogether.