Snails move slowly because, as gastropods, their only method of locomotion is to use their powerful stomach muscles as a kind of foot by flexing and releasing tension in said muscles. This process is reliable but makes the snail a very slow insect without any agility or ability to maneuver quickly, weaknesses offset by their durable shells, which they use for protection.
Snails secrete trails of mucoid slime that help them glide without resistance over even rough surfaces. These trails of slime also allow snails to move up vertical and near-vertical surfaces such as walls and the trunks of trees, as the snails adhere to their own trails.
The movement of a snail's stomach muscles is a lengthy process. The muscles must expand and contract in order to propel the snail forward, and the snail's weight relative to the power of its flexion harshly limits its top speed. Slugs are limited in the same way and use the same method to move.
Snails feed on vegetation such as leafy greens, grass and other common plants. They are known for attacking gardens, breeding in damp places and making general nuisances of themselves on human property. Their slow speed makes them easy to gather and reposition.