Article continues below advertisementWith eyes constantly on them, it's no wonder members of the royal family have some subtle signals to speak to each other when they know they're being filmed. The aforementioned was put on display on Wednesday, December 3, when the Prince and Princess of Wales were filmed during a tour of a special German exhibit from the Royal Collection at Windsor Castle. Prince William was caught subtly rubbing Kate Middleton's back as she was speaking to someone off camera - a move that is said to be a gesture to tell his wife to wrap up her conversation.