We're talking about microscopic, self-replicating robots that can invisbily build--or destroy--anything.
When something like this shows up, ninety-nine times out of a hundred it's a speck of dust (one can't be too clean in the workplace) or a microscopic defect in the emulsion; but there is also the minuscule probability that it's a nova, and one has to make a report, subject to confirmation.
