I was reading a piece by David Sedaris the other day and it contained a passage wherein something happened and a character in the story reacted to it, which is not unusual except that he somehow found space inbetween to write 2-3 additional sentences without interrupting the flow of the story. In Understanding Comics, Scott McCloud talks about this idea in the context of comics:
See that space between the panels? That's what comics aficionados have named "The Gutter!" And despite its unceremonious title, the gutter plays host to much of the magic and mystery that are at the very heart of comics! Here in the limbo of the gutter, human imagination takes two separate images and transforms them into a single idea.
While McCloud relies on human imagination to fill in the gaps, Sedaris recognizes one of the endless numbers of gaps that may be filled in a prose narrative and does so great effect.