This is part of an illustration from “Gauge Theories of the Forces between Elementary Particles”, by Gerard ‘t Hooft, from Scientific American, published in 1980.  I think it quite astounding that one can convey the concept of the “ghost of a massless scalar boson” by a simple dotted circle.  This implies that one can illustrate a massless scalar boson (of the non-ghost variety) with a full circle (as dotting a line is clearly the indication of ghostiness), and, indeed, that full circle appears elsewhere on the page.  This implies to me that physicists are much more self-assured than biologists – I think most biologists would feel silly drawing a dotted circle and calling it the “ghost of a massless scalar boson”.  And, really, the name itself is so appealing – we biologists need to name things as evocatively as “massless scalar bosons”.  Maybe if we did, we too could acquire billions of dollars for our research.