It pays to serve rodent. CBS’s “Survivor” was by far the No. 1-rated show on Wednesday, when that night’s episode featured the castaways dining on grilled rat. Not that the segment went down well with everyone. The animal-rights group People for the Ethical Treatment of Animals plans a protest outside CBS’s New York studios on Friday, according to news reports. The network is ready for them. On Thursday it issued a statement saying, “we truly believe that our viewers recognize that hunting and fishing as a means of sustenance have been acceptable since the dawn of time.” Furthermore, the show’s viewership continues to rise. The first week it commanded 15.5 million watchers; the second week, 18 million; this week, 23.1 million.