Continuity mistake: After Ted's Saturday night party (second of the three), when Ted, Lily and Marshall are sitting on the couch, numerous things change or suddenly appear behind them. Clothing is instantly on the back of the yellow chair and black chair, a wood chair appears, furniture moves, etc.
The Wedding - S1-E12
Other mistake: On The Wedding invitation it says the year is 2005, when it should be 2006 since the last episode was New Years.
Continuity mistake: Before Marshall proposes the gold foil is still on the bottle of champagne. He sets it down with the foil still on and they have sex on the kitchen floor. When they sit up, he grabs the bottle of champagne again and the foil is already off. (00:04:50)
Life Among the Gorillas - S1-E17
Continuity mistake: At the karaoke bar, when Marshall is deciding which song to sing, his beer bottle keeps switching hands between shots.
Continuity mistake: When Robin and Barney meet up for drinks, the amount of ash on the end of Barney's cigar goes up and down frequently between shots. (00:06:10)
Continuity mistake: When Lily drops the potato chips on top of the 'salad', we can see a few chips sticking up beyond the top of the bowl. The shot changes and now the chips are laid flat, with none sticking up over the top. (00:07:40)
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: In the opening scene at the bar, when Ted is debating whether or not to ask out Robin, Marshall's beer is in his hand when the camera is on him, but on the table when the shot is from behind him. (00:03:00)
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.
Other mistake: At the beginning of the series, Ted starts telling the story of how he met the mother of their children. When he starts describing how he met Robin, he doesn't reveal that it was not their mother until the end of the pilot. But children should have realised it wasn't their mother when Robin said she was a journalist and worked as a TV presenter. The kids knew their mom wasn't a journalist, so they shouldn't have been surprised at the end of the episode when Ted said "this is how I met your aunt Robin".
The Wedding - S1-E12
Plot hole: After Claudia's call, they decided that Lilly will meet her at the bar and the guys will meet Stuart. They're all at the apartment at the same time and the dudes have gotten to Stuart's apartment, convinced him to still marry Claudia and then go back to the bar right after Lilly gets there. And also giving a lot of time to Barney hitting on Claudia. There's no way that could happen in this order, they live right above the bar, Lilly was supposed to be there before Claudia.
Nothing Good Happens After 2 A.M. - S1-E18
Continuity mistake: When Ted arrives at Robin's apartment, he gets out of the taxi. Camera cuts to outside, and he opens the door and gets out again. (00:09:50)
Continuity mistake: When Ted is talking about getting a blessing from a pimp, Barney's drink just disappears from the table. (00:03:35)
Nothing Good Happens After 2 A.M. - S1-E18
Continuity mistake: When Robyn is leaving at the start, the dogs change place instantly. Note the Dalmatian. (00:01:30)
The Pineapple Incident - S1-E10
Continuity mistake: When Trudy takes Ted's phone she grabs it with 2 hands. Camera cuts and now she has one hand on her face. (00:17:35)
Matchmaker - S1-E7
Continuity mistake: In the opening scene at the bar, when Ted and Barney are discussing the idea of going to visit a Matchmaker, Ted's beer glass suddenly goes from being about a quarter full, to being nearly three-quarters full. (00:02:20)
