APAD：Which is which？which witch is which?

Which is which； 

'Which is which?' - often expressed as a question, asking for help in distinguishing two similar things or people. 

The first person to record 'which is which' in modern English was William Shakespeare, who used the expression in several of his plays, including Macbeth, 1605:

What is the night? Almost at oddes with morning, which is which.

Almost immediately after that line, Shakespeare gave the stage direction 'Enter three Witches'. He didn't however go on to make the play on words 'which witch is which?' - that had to wait until the 20th century. The first example I can find occurred, appropriately, on Halloween 1931, in the Wisconsin newspaper The Appleton Post-Crescent:

There's nothing like a Halloween moon to make people wonder which witch is witch.