Lady Samsara wrote:
I have a huge Apple snail and he does the very same thing, though I
have never seen the mucous trail on him. I'm not sure if they can
fill up with air or something to float, but it seems so, as I see
bubbles coming out of his shell when he does this. He will glide
across the tank, current taking him afloat, and then crash-land at the
bottom. Sometimes to make the game more interesting, he will grab just
a shred of a plant and stable himself, only to keep motoring on. As
Donald said, it must be intentional because he does it over and over.
I must say, he is probably my favorite in the tank, his antics keep me
entertained all the time. Silly snails!

Remember - snails do breath, through either their lungs or their gills
(depending if they are in water or not)