James Harto successfully performed this two-person-code mind-reading act together with his wife Catherina Wren for many years.

From the introduction:

Perhaps the most entertaining part of this branch of mystification is where the operator in some mysterious manner conveys to the assistant on the stage a question that has been whispered in the operator’s ear by a person in the audience and the assistant on the stage gives some kind of an answer that satisfies the spectator, that the assistant actually received the substance of the question that was whispered by him or her.