Garden snails, Helix aspera, attached to the surface of a sheet of glass, seen from the underside. The picture shows the large muscular foot that is characteristic of snails. The foot secretes a slime that lubricates the motion of the animal and also provides adhesion where necessary ( as here ). The animal moves by generating waves of muscular contraction in its foot (pedal waves). In motion, the foot elongates along the direction of movement. In this picture the snails to the top and bottom of the frame are about to move from left to right. The foot of each is elongating, with the narrow end (left) away from the direction of movement. The faster a snail moves, the longer its foot becomes. The groove visible to the right of the two elongated snails marks the position from which the head will emerge.