Continuity mistake: When Robin and Lily are talking in the apartment of Barney's date, Lily's hand moves instantly between shots from resting on her shoulder, to resting on the handbag by her side.
Continuity mistake: During the scene in "Marshall and Lily's part", after they leave the bathroom, we can see Robin and Virginia (Ted's Mom) talking in the back. Their hand motions do not match the later scene of the "Robin and Ted's part". Obviously, they were shot separately.
Continuity mistake: At the courthouse, when Lily is eating red licorice from the vending machine, the piece she is eating gets longer between shots.
How Lily Stole Christmas - S2-E11
Continuity mistake: When Marshall and Ted are on the phone to one another, the string from Ted's hoodie changes position between shots, much of this may be because he is moving his hand due to being on the phone. However the right string goes back and forth from being caught on the collar of his jacket to hanging straight down over his jacket just before he is on the phone to his mother.
Continuity mistake: When Lily, Ted and Robin are at the bar discussing Ted's building design, Lily's drink keeps moving between shots. Sometimes it is in her hand lifted towards her mouth, whilst in other shots it sits on the table.
Continuity mistake: When they are watching the music video on the small screen on the table, there is a bottle of JT Cola next to the screen in the close ups. When it goes to a wide shot, it is suddenly replaced by a beer bottle. However, in the previous shot before the commercial break it is a JT Cola bottle in the same spot as the beer bottle.
Continuity mistake: When Ted sits down to talk with Hammond Druthers after discovering that Druthers is living at the office, Hammond pours them both a J. Buckley whiskey. When Hammond places the bottle down the label is facing towards Ted. The camera then swaps to Ted and upon swapping back to Hammond, the label is facing away from Ted. Hammond is describing his wife as "quite mannish." The camera swaps to Ted. Upon swapping back to Hammond, when he continues with "She gives me what I need", the bottle has been rotated so that the label faces towards Ted again. (00:11:40)
Continuity mistake: At the apartment when Marshall gives Lily the red cocktail, the green paper umbrella moves from facing away from Lily to facing towards her between shots.
Continuity mistake: In the scene when Lily yells at Robin, because Lily thinks her wedding is ruined, her hair changes. When Lily screams "Of Course I'm not okay." there's only one stray of hair hanging over her left shoulder, but a few seconds later when she screams "Oh grow up Robin." much more hair is hanging over her shoulder. (00:08:15)
Moving Day - S2-E18
Continuity mistake: In the final scene when Barney is reading his top ten list, the piece of paper moves from his left to right hand and back in an instant between shots,.
Continuity mistake: When Marshall and Lily approach the reception desk at The Wedding chapel, Marshall's cocktail moves from his right to his left hand instantly between shots. (00:07:55)
Chosen answer: She was finally shown at the very end of the last episode of season 8, continuing into season 9. The actor's name is Cristin Milioti: http://www.imdb.com/name/nm2129662/.
Knever