In the scene where Fran, Steve and Mary are in the car driving to the vineyard, if you watch, Mary starts out in the seat behind Steve. When Fran and Steve are talking about the wedding songs, they ask her if something was wrong, and Mary is sitting in the seat behind Fran. She switches back to being in the seat behind Steve. When Steve swerves over into the other lane, Mary is back in the seat behind Fran. You get the picture. Basically every other scene when the camera flashes back to the back seat, Jennifer Lopez is in a different seat.