Continuity mistake: When Barney is crouched down, leaning against Robin's chair, the money in his right hand vanishes between shots.
Continuity mistake: When Robin is talking to her boss about his dog, the pens and pencils in the holder on his desk change depending on the camera angle.
Continuity mistake: After Natalie throws spaghetti at Ted, the amount and position of the spaghetti pieces changes instantly between shots.
Continuity mistake: When the gang are discussing what Ted should say to break up with Natalie, the amount of beer in Marshall's glass goes up and down between shots.
Continuity mistake: When breaking up with Natalie, her hands are constantly changing position between instant cuts. (00:18:30)
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