animal garden grass mucus shelless slimy slow slug snail flagstone glint lubricant path silver Slime trail wander weave animation art Co-vid 19 graphic design green illustration macro photography organism pattern virus water calcium carbonate coiled coiled shells crawling exoskeleton eye stalks eyes friction garden snail gastropoda helix aspersa herbivorous land snails locomotion logarithmic spiral mantle mollusk movement muscular foot olfactory organs ommatophores radula retractable retracting ripple rippling shell skin spirally tentacles terrestrial snails textured surface unsegmented