I found this on the Kittynet

A visiting preacher was invited to give the sermon at a local church. When someone in the congregation would respond with "Amen" or "That's right preacher," the guest pastor would get carried away and launch into an extended sermon. Finally, the exasperated host pastor started responding to remarks by the guest preacher with "Amen, Pharoh!"......which unnerved the guest preacher. After the service the guest preacher asked the host pastor, "what did you mean when you said, 'Amen Pharoh?' " His host replied, "I was telling you to let my people go."