With the appearance of The Rat it might be necessary to revise Grass's "Danzig Trilogy" to "Tetralogy." This is the fourth novel set in the Danzig environment, and it embodies the same themes as the earlier works. Oskar Matzerath has made cameo appearances in a number of works since The Tin Drum, but only in The Rat is he again a substantial character. In Grass's 1963 play, Flood, he used rats as a metaphor for mankind. The Flounder (1977) is also explicitly referred to in the description of the Baltic Sea jelly-fish/ Vineta expedition.