When the yoga teacher says "moving into Warrior 1", the bridesmaids all do Warrior 2 pose instead.
While Tess is playing golf with the father of the bride, 1:05 into the movie, he received a call in the sand trap from the wedding planner who allegedly quit earlier in the movie.
Michael says that the blue jewelry matches Tess' eyes, but her eyes are green.
The groom's and groomsmen's boutonnieres are on the wrong lapel of their tuxedos. They should always be worn on the left lapel above the heart.
Safety Tip 101: Never walk down stairs with hands in your pockets.
On the drive from the airport, mountains are clearly visible through the car windows. There are no mountains in Chicago.
Tess does not rehearse her slide show for the rehearsal, which she certainly would have done.