The conversation between human and AI assistant.
What are the best riddles by the Riddler (Batman)?
Those are all really good! Has the Riddler ever stumped Batman with one of his riddles?
Yes, there have been times when even Batman has been stumped by the Riddler's riddles. One example is when the Riddler asks Batman, "What begins with an 'e,' ends with an 'e,' but only contains one letter?" The answer is "envelope."