To save energy, snails re-use mucus trails laid down by other snails:
Snails create trails of mucus to that help them glide across the ground, mainly in search of food or a partner, but making all that mucus uses up a lot of energy.
“Snails expend a lot of energy, probably a third, creating mucus,” said Mark Davies of the University of Sunderland, lead author of the study published in the journal Proceedings of the Royal Society B. “This process is very taxing indeed—much more so than walking, swimming or flying.”
Davies and his colleagues studied marine snails off the coast of Britain and discovered that to save some of this vital energy, the snails sometimes follow the existing mucus trails laid down by other snails to get around and so only have to create a fraction of the mucus needed to make a new trail.
http://www.livescience.com/animalworld/070228_snail_mucus.html - via Scribal Terror