They have long mating rituals. Once they are aroused genitals come out of their face/neck and couple together.
Then they stay like that for hours, like many hours, you cannot separate them because their genitals are so deep inside their body that you'll may kill them.
After that they part ways like nothing.
Source: I have pet snails and have watched them having sex several times. To my defense I also let them watch when I have sex.
Why, you jacking off to a snail shitting itself or something?
Edit:
"Please put an NSFW tag on this. I was on the train and when I saw this I had to start furiously masterbating. Everyone else gave me strange looks and were saying things like “what the fuck” and “call the police”. I dropped my phone and everyone around me saw this image. Now there is a whole train of men masterbating together at this one image. This is all your fault, you could have prevented this if you had just tagged this post NSFW."