When the Reverend Smith is sitting beside the piano in the Gem (the first time), you can see Ray McKinnon's iris and pupil through the contact lens mock-up of his lazy eye.
Reverend Smith recites several lines of The Prayer of Saint Francis; however, this prayer was written in 1912 and first appeared printed in English in 1927, decades after the show takes place.
At 24:53 the camera pans to the left revealing an open end scrim flag mounted to diffuse the light.