The slides C3 and L4 have probably developed from the same original image, belonging to a series of underground images taken during the construction of the LEP tunnel, like the one below. It was common to produce multiple copies in slide format for an iconic image. The slides were then distributed as requested to illustrate the presentations or documents. The action of mould has produced different effects on C3 and L4. Although stored together, the slides underwent a unique and irreproducible transformation, caused by the digestion of enzymes and the single-cell cloning of microorganisms, in a manner that was a priori totally random. Fractal plots appear here and there depending on the goodwill of the microorganisms.