As tools, digital photographs produce a mental event reshaping perception, generating a use-wear redescription of prehistoric people calculating shell net weight systems of at least ten grams. String is essential in making fishing nets with weights. We address how altered photographs can create false memories, and show that strategically reconfiguring digital shell images, in alignment with prehistoric tool use-wear studies, a better visual guide is introduced. This might explain associated precuneus brain evolution involved in bimanual processes, mathematical calculations, and spatial thinking, preceding by about 30,000 years the bow and arrow. As etched on the Blombos ochre stone, in figure 1, the net had to have a diamond shape to which a string of shells was attached, preventing shells from entangling. Digital editing, in figure 2,then helps us mirror the prehistoric cognitive style and visual grammar describing how the net would look in figure 3.