What's a joke in this sentence ?

[Assassin]

His face was drawn but the curtains were real.

P.S: I found it in the book "The Curious Incident of the Dog in the night-time" by Mark Haddon. The narrator just says there is a joke in this sentence but I still can't get what the joke is -____-!

Thanks for explaining !

[bhaisahab]

His face was drawn but the curtains were real.

P.S: I found it in the book "The Curious Incident of the Dog in the night-time" by Mark Haddon. The narrator just says there is a joke in this sentence but I still can't get what the joke is -____-!

Thanks for explaining !

It's a play on the word "drawn" we draw curtains when we open or close them, someone whose face is drawn looks tired or ill, also when we draw something we make a picture of it, so "His face was drawn; it was not real, it was a picture of his face, but the curtains were real."

[Assassin]

Quite understood.
Thank you, anyway