Continuity mistake: When Steph is telling Ted that she used to star in adult films, we see her pick up the mini corn with her chopsticks from one angle, then the shot changes and she picks it up again. (00:02:30)
Continuity mistake: In the final scene at the bar, Barney is seen eating the olive from his drink and discarding the stick. A second later, when the shot changes, the olive and stick are back in his glass.
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: When Barney is crouched down, leaning against Robin's chair, the money in his right hand vanishes between shots.
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