Other mistake: When the girls are sitting in the common room on the night Giselle shows them the contraceptive, Betty says, "Do you realise November 2nd is three weeks from now?" Yet, the University newspaper with Betty's nasty editorial shown on screen the next day is dated September 19th. (00:18:43 - 00:23:53)
Other mistake: In the scene where Betty and Joan are in the kitchen after dinner, we see the coffee percolating in the pot but never see Betty pour the coffee into the china pot before taking the tray into the living room.
Other mistake: Betty's mom is requesting a change in the table setting, eg. no candlesticks, glassware trimmed with gold etc. You then see the actual wedding happening and see candlesticks and glassware without the gold rim.
Chosen answer: There is a short discussion (I believe between Kirsten Dunst and Julia Roberts) about things not always being what they seem. They are speaking about the girls' lives, but it also is symbolic of the Mona Lisa smile. Whether she is really smiling is left up to the person viewing the portrait: is she smiling because she is happy? Is she trying to cover up grief/sorrow? Is she smiling at all?
Macalou