arch atlas bb bengal berlin brown bull charles crouching death deficit dollar donald elvis extra fallen film fish fishing gamma gates guardian hook inter lame larry lima loan louis mallard manta merlin mo monaco morgan morning mosquito murray north oz panda patrick paul peking peter phoebe polar pool prometheus radagast rhea rights rock rodney ron siberian silver sofia sparrow sting teddy tony whale woods
Step 1: Sort the words into 16 groups of four. All of these groups have a one-word title, which is always plural.
Step two: Sort the titles into four groups of four. What is the common theme?