The Food Poisoning Scene
Did they not try on the dresses and then all get violently ill right after eating the lunch that supposedly got them all sick? Because of the nature of food poisoning, especially food poisoning which causes diarrhea (Which their illness obviously did), it usually has an onset time of over 12 hours. There just isn't enough time for the bacteria to get where it needs to go in the digestive system, and then to multiply to a point where it can have an effect on the body. They all got violently ill like an hour or two after lunch. In real life, that just doesn't happen.
Rylant