There is a snail crawling across this woman's nipple. There are people in the world who enjoy having snails crawl across their nipples. Sometimes, these people wake up in the morning and think, "Gee, I really want to have a snail crawl across my nipple." Or maybe this premonition occured to them in a dream. In such case, the events would possibly unfold like this, "Gee, I have a snail crawling over my nipple." Actually, snails don't crawl. They don't slither, run, walk, jog, waltz, jump, or climb, either. Therefore, there's nothing left but for a snail to float. Therefore, that snail isn't really touching anybody's nipple and this was just a waste of time.
The moral of this lecture is to find out the term for snails' means of mobility.