Continuity mistake: When Rachel and Finn are doing their toast, the amount of cider in the glasses changes between shots.
Deliberate mistake: Many times throughout the show, a large bandage or makeup blot is visible on Lea Michele's right wrist, which is used to cover up her "I Believe" tattoo. This is most visible during "Don't Rain On My Parade" and her "Poker Face" and "For Good" duets.
Continuity mistake: During "Don't Stop Believing" at the line "He took the midnight train going anywhere," Rachel extends her hand with her palm facing the floor. In the next shot, it instantly changes to her palm facing the seats of the auditorium. (Timecode listed for the director's cut of the episode.) (00:44:00)
Continuity mistake: During "Never Been Kissed", just after Sue activates the confetti cannons and is talking to Will, the amount of confetti on Will's shoulders changes between shots.
Continuity mistake: When Mercedes is singing "Bust Your Windows", the blue rags on Kurt's car behind her change position several times. Also, Kurt is at first looking up at the hole in his windshield, then has his head down on the hood, and then is looking up at the hole again, over a series of 3 or 4 shots.
Continuity mistake: At the end of the episode when Kurt and Blaine are sat in the Lima Bean, the position of Blaine's hand where it props up his face changes. Whenever we see Blaine from the front, his fingers are curved slightly, but when we see Kurt (and the back of Blaine's head), his fingers are held straight so they do not interfere with the shot.
Continuity mistake: During season 2 "Never Been Kissed", just as the Warblers begin to sing "Teenage Dream", a boy with a briefcase walks in front of Kurt, heading towards the left. Two shots later, the same boy with the breifcase walks left in front of him again.
Continuity mistake: In "The Power of Madonna", during the Cheerios stilts routine, as the people on stilts lift one leg one after the other, they are in a V shape, and there are both girls and boys on stilts. Yet in the very next shot, as the people on stilts swing the other Cheerios around, there are only 3 Cheerios, all guys, on stilts, and they are in a straight line.
Laryngitis - S1-E18
Continuity mistake: During "Laryngitis", Puck pulls Mercedes up to come sing "Lady is a Tramp" with him. Yet in the very next shot, just as she starts singing, she stands up again. So she stood up twice.
Continuity mistake: Puck butters the floor, and as Kurt slips and falls, The Substitute is not where she had been standing. The next shot, she's still there. (00:07:45)
Other mistake: During "Asian F", when Kurt is filling out his NYADA application, he lists his address as "415 Whitman Avenue". Yet during "The First Time", when Rachel is approaching Finn and Kurt's house, the number on the house is 291.
Continuity mistake: During "Blame It on the Alcohol", when Quinn is shouting at Puck, her hair is messy and straight. Yet a little while after, during "Don't You Want Me", her hair is curly and styled perfectly.
Continuity mistake: During "Last Name", just as April is singing "We left the club," she backs up into Kurt in the wide shot, yet during the very next shot she is still a couple of feet away from him.
Sectionals - S1-E13
Continuity mistake: In episode 13 of season 1 (Sectionals), during the five way split screen, the extras behind Mercedes and the ones behind Tina are the same but have different movements.
Continuity mistake: While the Warblers are singing "Teenage Dream", during the closeups of Kurt, his bag's strap is under his jacket's lapel, but in the long shots, it's on top of the lapel.
Continuity mistake: When Kurt goes to sit down and play the piano for Finn, he is wearing cream coloured pants. Yet in the closeup shot of his hands, he is wearing jeans.
Continuity mistake: In 3x09, while Kurt and Blaine are singing "Let It Snow", the fire is going. When they finish the song and notice the "audience", it's out. When Kurt is opening his present from Rachel, it's going again.
The Purple Piano Project - S3-E1
Continuity mistake: Blaine has finished singing and the piano is ablaze. Several Club members are seen sitting at the table, then a different view shows only Rachel and Kurt and empty seat spaces where others were sitting.
Continuity mistake: When singing in the choir room with Finn, Rachel's necklace changes from inside her dress to outside several times.
Answer: According to IMDb.com, Ian Brennan, one of the "Glee" writers and producers, is listed as the uncredited narrator voice.
Michael Albert