appeared in the British underground magazine Cyclops. Not every intertextual link in the series was planned by Moore, who remarked that "there's stuff in there Dave had put in that even I only noticed on the sixth or seventh read", while other "things [...] turned up in there by accident." A stained smiley face is a recurring image in the story, appearing in many forms. In The System of Comics, Thierry Groensteen described the symbol as a recurring motif that produces "rhyme and remarkable configurations" by appearing in key segments of Watchmen, notably the first and last pages of the series—spattered with blood on the first, and sauce from a hamburger on the last. Groensteen cites it as one form of the circle shape that appears throughout the story, as a "recurrent geometric motif" and due to its symbolic connotations. Gibbons created a smiley face badge as an element of The Comedian's costume in order to "lighten" the overall design, later adding a splash of blood to the badge to imply his murder. Gibbons said the creators came to regard the blood-stained smiley face as "a symbol for the whole series", noting its resemblance to the Doomsday Clock ticking up to midnight. Moore drew inspiration from psychological tests of behaviorism, explaining that the tests had presented the face as "a symbol of complete innocence". With the addition of a blood splash over the eye, the face's meaning was altered to become simultaneously radical and simple enough for the first issue's cover to avoid human detail. Although most evocations of the central image were created on purpose, others were coincidental. Moore mentioned in particular that on "the little plugs on the spark hydrants if you turn them upside down, you discover a little smiley face". Other symbols, images, and allusions that appeared throughout the series often emerged unexpectedly. Moore mentioned that "[t]he whole thing with Watchmen has just been loads of these little bits of synchronicity popping up all over the place". Gibbons noted an unintended theme was contrasting the mundane and the romantic, citing the separate sex scenes between Nite Owl and Silk Spectre on his couch and then high in the sky on Nite Owl's airship. In a book of the craters and boulders of Mars, Gibbons discovered a photograph of the Galle crater, which resembles a happy face, which they worked into an issue. Moore said, "We found