Are you supposed to be normal?

In 1967 Harold Pinter received this letter from a woman who could not comprehend the meaning of his play The Birthday Party.

Dear Sir,
I would be obliged if you would kindly explain to me the meaning of your play, The Birthday Party. These are the points which I do not understand:

1. Who are the two men?
2. Where did Stanley come from?
3. Were they all supposed to be normal?

You will appreciate that without the answers to my questions, I cannot fully understand your play.
Yours faithfully,

See Pinter's clever reply at Letters of Note