On the episode where Monica gets her wedding dress, in the beginning she picks one out at an expensive store so she can buy it at a discount store. When she goes to the discount store, she buys a different dress than the one she picked out. Then, when they show Monica, Phoebe, and Rachel admiring the dress at Monica's apartment, it is the same dress she picked out in the beginning. I love Friends, but somebody should have caught this one!