Snail sex is interesting in large part because snails are hermaphrodites. When every member of a species is equipped with both sets of reproductive organs, the act of mating gets complicated. Each partner sorts out their sex role on the fly.
In garden snails, the act starts with a “love dart” fired by a potential partner about half an hour before copulation. The dart gets embedded in one or both partners, and it contains hormones that prevent the darted snail from killing incoming sperm. Because sperm is passed in both directions, the snails end up in a battle to determine which one's sperm will live—and thus, which snail has to end up carrying fertilized eggs.
For an Ultra HD look at the sex lives of snails, watch the video above. If you want to know more about these fascinating animals (which have thousands of teeth, by the way!), read our list of facts. And if you want to know even more weird facts about getting it on in the animal kingdom—like which creatures engage in penis fencing and which use urine as part of mating rituals—check out this list.
A version of this story ran in 2017; it has been updated for 2023.