In some scenes (usually outdoor ones), words appear with the letters themselves in mirror image, while in others (usually on signs or newspapers), while the words are spelled backwards, the letters themselves appear normally.
Although most of the shots of the outdoor scenes are mirrored (lettering on car numberplates and shops appears backwards), a couple of shots aren't: the shot of the white van Rimmer and Kryten ride in as it goes backwards down the street and the shots of the van that Lister and Cat get a lift in.
At the start of Kryten and Rimmer's act, Rimmer says that Kryten will eat an egg in forwards talk. The crowd react with amazement, but the audience would only understand backward talk and therefore would not have been able to understand what Rimmer had said.
While Rimmer is testing Kryten in Starbug, he points to a picture which Kryten identifies as a "binary star." Rimmer then asks "what's that one?" while pointing to the same page and identifies it as "quite obviously a blue giant about to go supernova," but he is pointing to the same page Kryten already identified as a "binary star."
The crew go to a universe where time is running backwards. Inevitably, this means that there are many errors made with regard to the correct order of certain events, many of which are integral to the plot.