Continuity mistake: Monica chooses a wedding dress at an expensive boutique, then later goes to a discount store to buy the same-style dress at a half-off sale. The dress she buys is different from the one in the boutique, having wider and frillier straps. When she tries it on later at the apartment, it is now the same style as the one at the boutique.
Continuity mistake: When Monica is talking to Chandler about nothing having gone wrong, Chandler's arms are crossed. The camera cuts, and his arms are down by his side.