In her book Toward Zero, author Agatha Christie has the following dialogue:
Kay said: ‘I don’t like my colour scheme in the livingroom. Can I have it done over, Nevile?’
‘Anything you like, beautiful.’
‘Peacock blue,’ said Kay dreamily, ‘and ivory satin cushions.’
‘You’ll have to throw in an ape,’ said Nevile.
‘You can be the ape,’ said Kay.
What on earth is that supposed to mean, "throw in an ape"? I have no idea. Is that an expression?