You say "I think we're going to go now Mom." As you get up to go out the door Mom says "Oh wait, before you go. I've got something for you". She goes and brings back some magazine or DVD for you to watch. This devolves into another 20 minutes of conversation. Then you begin moving toward the door again when she says "Oh wait, do you want to take some pie with you?" you politely say yes. This devolves into another 20 minutes of conversation after which you may actually leave. Warning: There may also be a another preleave as you attempt to get into your car.