During particularly dry weather some snails will only touch the ground with part of their "foot" at once. In effect moving more like a desert snake in the image below. They do this to reduce moisture loss. Even though it is still a continuous motion it leaves a discontinuous trail. the same number of these points of contact are present the entire time at no point does it leave contact, think of it more like high stepping. This behavior is sometimes called "jumping" even though it has nothing to do with actual jumping.