You may already be familiar with the production by some species of snail of 'love darts', small calcareous spears that a mating snail fires into its partner. The function of the love dart is still not entirely understood, though it does seem to improve sperm uptake by the snail being darted: whether by lowering its ability to resist insemination, or because snails are mini-masochists that get off on being stabbed, I couldn't say. Most textbooks describing the use of love darts will (at least effectively) base their description on the common garden snail Cornu aspersum (or Cantareus aspersus, or whatever the heck we're supposed to be calling it these days), which leaves its love dart embedded in its partner's skin. Bradybaenids whose mating behaviour has been studied, however, do things a bit differently. Instead of abandoning its dart after a single firing, bradybaenids withdraw the dart and use it to stab their partner repeatedly, making it more of a love shiv than a love dart. And when I say repeatedly, I mean repeatedly: mating pairs of Euhadra subnimbosa would, on average, stab each other with the dart over 3300 times (Koene & Chiba 2006). So vigorous is the stabbing, in fact, that the dart pierces straight through the recipient and emerges through its foot! For those with JSTOR access, a video of the process can be seen at http://www.jstor.org/stable/10.1086/508028. And trust you to go rushing to watch a film of gastropod SM.
Koene, J. M., & S. Chiba. 2006. The way of the samurai snail. American Naturalist 168 (4): 553-555.
Wade, C. M., C. Hudelot, A. Davision, F. Naggs & P. B. Mordan. 2007. Molecular phylogeny of the helicoid land snails (Pulmonata: Stylommatophora: Helicoidea), with special emphasis on the Camaenidae. Journal of Molluscan Studies 73: 411-415.