When Ted and Mary are arguing about Anastasia, the amount of water in the pitcher and glass she keeps drinking from varies.
When Ted goes into their darkened bedroom to talk to Mary after the concert - basketball game mix-up, the "moonlight" in the window goes out a beat before Ted can turn on the bedside table lamp.
After 13 year old Harriet catches the bouquet and says "Hurray. I'm going to be married next." her MOTHER says "You're going to have to get out of the fourth grade, first." A 13 year old would be in the 7th or 8th grade. Her mother surely realizes that.