Prison Quartet

Said a preacher:

While I was preaching in a church in Mississippi, the
pastor announced that their prison quartet would be
singing the following evening. I wasn't aware there was a
prison in the vicinity and I looked forward to hearing
them.

The next evening, I was puzzled when four members of the
church approached the stage. Then the pastor introduced
them.

"This is our prison quartet," he said, "behind a few bars
and always looking for the key."