Last Sunday we took a walk along a wooded park in a slightly rural area. Near the end of the park there were some isolated houses and in front of one of them was an old, dirty pickup truck.
I noticed some peculiar marks on the dust-covered hood of the truck.
On close inspection, they turned out to be slug feeding tracks.
These slugs normally graze on layers of blue-green algae (cyanobacteria, actually). But what was covering the hood of the truck didn't look anything like algae to me. It was for like a blackened crust of street dust. There must be something nourishing in it, though.
Here is another post about the discovery of slug tracks in an unexpected spot.