(at around 20 mins) When Lily and Robin argue at the bar, the bartender serves the people in the booth behind Robin. A split second later, the bartender is not there. And right after that, the bartender instantly reappears.
As Barney is asking Lily who would woo, the man in the back is mouthing his dialogue.
When Marshall is shown in his office, you can see his diploma on the wall. The diploma is from Ohio Wesleyan University, but Marshall, Ted, and Lily went to Wesleyan University.
Marshall, who hails from Saint Cloud, Minnesota, refers to himself as an athletic champion of Nicollet County. The city of Saint Cloud is located in Stearns County. While Nicollet County is the name of a county in Minnesota, the two are located hundreds of miles apart, making it unlikely that Marshall would compete in an athletic contest in Nicollet County.