A footprint is shallow relief, two or three centimetres at most, and it shows up only when the light comes in low. At noon the same beach reads as a flat sheet; by five every heel mark has a shadow as long as a finger and the whole surface turns into a text. Going back at the right hour is less about the colour than about the angle that makes depth visible.
Sand and snow keep the record differently. Dry sand collapses at the edge, so a print rounds off within minutes into a soft dent with no rim, while wet sand holds a sharp lip until the tide comes up and takes the entire page at once. Snow keeps the cleanest edge of the three, and the inside of a print goes faintly blue, because what falls into the hollow is sky light rather than sun.
The tracks worth looking at are usually not human. A bird crossing a dune leaves three-pronged marks at an even stride, a hare leaves paired sets that tell you which way it was going, wind leaves ripples that erase both. On a screen this kind of picture holds up because it is quiet and still carries an event: something passed here, and by the next morning the surface was blank again.
