The uses of mucus
The silver trail is a road, a glue, and a message. It is also expensive, which is why other snails reuse it.
How land snails breathe
The small hole on the right side of a garden snail is a lung opening. Many pond snails use a version of the same trick.
Eyes on stalks
The eyes at the tips of the upper tentacles can tell light from dark and not much more. Smell does the finer work.
How a shell is built
The shell grows only at the lip. Calcium carbonate, a protein coat, and a spiral that keeps its shape as it gets larger.
The body under the shell
A garden snail is a muscular foot, a mantle that builds the shell, and a head with eyes on stalks. The shell is part of the body, not a house it found.