Once they find a dark damp spot to hide out on dry days, they will usually come back to that same spot, preferring to hide alone. They can fit into amazingly small spaces, this probably helps them to find enclosed areas that are still damp when most others have dried out With only one muscular foot, a slug moves slowly. How it moves can be seen when you place a slug on a piece of glass and look at it from underneath. Small horizontal waves of muscle move from the back to the front of the animal, allowing it to glide over a surface. A slug can travel over a razor blade or sharp edge of glass without cutting itself because of the slime that covers the foot.
Slime has many functions.
One is to keep the slug's skin moist so it can breathe through it. A slug breathes through its skin and just like the insides of our lungs, the skin must be moist to exchange gases. The slime gathers moisture out of the air like a sponge on damp days and out of the soil under logs on dry days. A second function of the slime is to protect the slug from predators. They simply hump up their body to make a bigger animal and produce a thick milky mucous.